National Transmission System

The United Kingdom's National Transmission System is the network of gas pipelines that supply gas to about forty power stations and large industrial users from natural gas terminals situated on the coast, and to gas distribution companies that supply commercial and domestic users. It covers Great Britain, i.e. England, Wales and Scotland.

Ownership

The transmission network is owned by National Gas, which is owned by Macquarie Asset Management. Agreement was reached in July 2024 for Macquarie to buy National Grid’s final 20% stake, giving Macquarie full ownership in the first quarter of 2025.
The changing ownership of the NTS reflects developments and corporate changes in the UK's gas and energy industries.

Gas Council and area boards, 1962 – 31 December 1972
British Gas Corporation, 1 January 1973 – 24 August 1986
British Gas plc, 24 August 1986 – 1994
Transco plc, part of British Gas plc, 1994 – 17 February 1997
Transco plc, part of BG plc, 17 February 1997 – 1999
Transco plc, part of BG Group plc, 1999 – 23 October 2000
Transco plc, part of Lattice Group plc, 23 October 2000 – 21 October 2002
Transco plc, part of National Grid Transco plc, 21 October 2002 – 31 January 2023; renamed National Grid Gas plc on 10 October 2005
National Grid Gas plc, owned by Macquarie, BCI and National Grid, from 31 January 2023; renamed National Gas Transmission plc on 6 February 2023
History

Origins

The system originated in the construction during 1962–3 of the high-pressure methane pipeline from Canvey Island to Leeds. Imported liquefied natural gas from Algeria was turned into gas at the Canvey terminal and supplied to the pipeline, providing eight of the twelve area gas boards with access to natural gas. The gas was initially used to manufacture town gas, either as a feedstock in gas reforming processes or to enrich lean gases such as that produced by the Lurgi coal gasification process.
The pipeline was in diameter and operated at 1,000 pounds per square inch. The pipeline had of spur lines, supplying gas to area boards.

Area board	Supply to	Diameter	Length
North Thames	Bromley/East Greenwich 'Tee'	14	15.5
North Thames	Bromley	10	2.5
North Thames	Slough
South Eastern	East Greenwich	12	3
Southern	Reading	8	49
Eastern	Chelmsford	12	19.9
Eastern	Hitchin	8	7
Eastern	Dunstable	6	8.5
Eastern	Watford	12	2.1
West Midlands	Coleshill	14	10.5
East Midlands	Sheffield	12	10
North Western	Manchester	14	24
North Eastern	Leeds	12	8

The Gas Council was responsible for this £10 million co-operative scheme and the construction details were a joint effort of the distribution engineers of the area boards.
LNG had first been imported to Canvey from Louisiana in February 1959, and piped to Romford gasworks as feedstock to a reforming plant.

UK natural gas

Natural gas was discovered on the UK continental shelf in 1965 and production started in 1967. The development of offshore natural gas fields is shown in the following table. Shore terminals were built to receive, process, blend and distribute the gas.

Field	Field type	Licensee or operator	Discovered	First gas onshore	Shore terminal
West Sole	Gas	BP	September 1965	March 1967	Easington
Leman	Gas	Shell/Esso, Amoco/Gas Council, Arpet Group, Mobil	April 1966	August 1968	Bacton
Hewett	Gas	Phillips Petroleum, Arpet group	October 1966	July 1969	Bacton
Indefatigable	Gas	Shell/Esso, Amoco/Gas Council	June 1966	October 1971	Bacton
Viking	Gas	Conoco/BNOC	May 1968	July 1972	Viking
Rough	Gas	Amoco/Gas Council	May 1968	October 1975	Easington
Forties	Oil + associated gas	BP	October 1970	September 1977	St Fergus
Frigg	Gas	TotalEnergies	June 1971	September 1977	St Fergus
Frigg	Gas	TotalEnergies	May 1972	September 1977	St Fergus
Piper	Oil + associated gas	Occidental group	January 1973	November 1978	St Fergus
Tartan	Oil + associated gas	Texaco	December 1974	January 1981	St Fergus
Brent	Oil + associated gas	Shell/Esso	July 1971	1982	St Fergus
Morecambe Bay	Gas + condensate	Hydrocarbons	September 1974	1985	Barrow

With the assured availability of natural gas, a government white paper on fuel policy in November 1967 proposed that natural gas should be immediately and more extensively exploited. The Gas Council and area boards began a ten-year programme to convert all users and appliances to operate on natural gas and consequently to discontinue the manufacture of town gas at local gasworks. In a pilot scheme, users on Canvey Island had been converted to natural gas in 1966.

Building the NTS

To exploit the availability of natural gas and to provide for more widespread distribution, construction began of a major new transmission network which became the National Transmission System.

Feeder pipelines – England

Gas from the West Sole field was first dispatched from the Easington terminal on the Yorkshire coast in July 1967, via Feeder No. 1 across the Humber to the East Midland Gas Board's gasworks at Killingholme. It was used to enrich low calorific value manufactured gas. Feeder No. 1 was extended to Totley near Sheffield where it connected to the 18-inch methane pipeline. UK natural gas first entered the NTS in July 1968.
Feeder lines from the North Sea gas terminals to the spine of the NTS were laid and brought into use as the shore terminals were constructed.

Feeder No.	Diameter	Length	From	To	Operational
1			Easington terminal	Scunthorpe and Totley near Sheffield, where it connected to the original methane pipeline.	July 1967/ July 1968
2			Bacton terminal	Brisley, Eye, Peterborough and Churchover near Rugby, where it connected to the original methane pipeline.	August 1968
3	36-inch		Bacton terminal	Roudham Heath, Cambridge, Peters Green, Whitwell near Hitchin, where it connected to the original methane pipeline.	October 1969
4	36-inch		Bacton terminal	Great Ryburgh, King's Lynn, Audley and Alrewas near Lichfield.	Autumn 1970
5	36-inch		Bacton terminal	Yelverton, Diss, Stowmarket, Braintree, Chelmsford and Horndon, where it connected to the original methane pipeline	Autumn 1971
6			Paull	Pickering, Westwood and Little Burden near Darlington	Autumn 1971
7	36-inch		Wisbech	Gosberton, Hatton, Old Warden, Tydd St Giles and Scunthorpe	1972
8	30-inch		Former Viking terminal	Hatton	July 1972

The No. 6 feeder runs via Pickering which received gas from a treatment plant for the onshore Lockton gas field.

Feeder pipelines – Scotland

North Sea gas first reached Scotland in Spring 1970 at Coldstream via an extension of the Leeds-Newcastle pipeline. This pipeline was then extended to Glenmavis near Coatbridge Lanarkshire where a natural gas liquefication plant was constructed.
A major set of pipelines were constructed in Scotland in preparation for arrival of gas from the Frigg gas field in 1977. From the St Fergus terminal in Scotland, two pipelines were laid via Bathgate to Partington and Bishop Auckland to connect to the NTS in England, a total pipeline length of. These lines were commissioned in 1976 and cost £140 million. Initially they carried gas from southern England into Scotland until the Frigg field began production via St Fergus in September 1977. Compressor stations are provided at intervals along the pipelines. A third 36-inch pipeline from St Fergus was completed in 1978, and a fourth pipeline in 1982.

Growth of the NTS

The NTS was extended from Leeds to Newcastle upon Tyne in early 1969. This line was extended to Coldstream in spring 1970 and then to Glenmavis, near Coatbridge, Lanarkshire.
The Wales Gas Board received natural gas supplies in 1969 through a 24-inch line from Churchover to Swansea via Wormington. North Wales was also connected in 1969 via a 24-inch/18-inch pipeline from Audley Cheshire to Maelor near Wrexham.
The South Western Gas Board received natural gas at the end of 1970 from a 24-inch/20-inch pipeline from Wormington to Exeter.
A 30-inch/24-inch extension of Feeder No. 3 runs to the west of London via Slough to Mogador, Surrey, and was commissioned in 1970. An extension of Feeder No. 5 runs from Horndon-on-the Hill, crosses the Thames at Tilbury and runs via Shorne to connect to Mogador, completing the South London ring main which became operational in early 1972.
In addition to these distribution pipelines, in 1971 the area boards began to supply natural gas directly to major consumers. For example, a 24-inch 17 mile 'spine' pipeline was constructed to ICI Ltd at Billingham, and the West Midlands Gas Board laid six similar 'spine' mains into industrial districts of Birmingham and the Black Country.
Most of the NTS was built from the late 1960s to the early 1980s.

Years	NTS mileage	Operational gas terminals	Compressor stations
1966/7	320	Canvey	0
1968/9	688	Canvey Easington Bacton	0
1970/1	1898	Canvey Easington Bacton	1
1972/3	2199	Canvey Easington Bacton Theddlethorpe	4
1974/5	2308	Canvey Easington Bacton Theddlethorpe	9
1976/7	2915	Canvey Easington Bacton Theddlethorpe St. Fergus	10
1978/9	3047	Canvey Easington Bacton Theddlethorpe St. Fergus	11
1983	3200	Canvey Easington Bacton Theddlethorpe St. Fergus	14

Later feeder mains not described above include:

Feeder No.	From	To	Year commissioned
9	Easington	East Ilsley	1983–86
9	Brocklesby	Stallingborough
10	Bathgate	Glenmavis
10	Thrunton	Saltwick
11	Bathgate	Longtown
12	Kirriemuir	Longtown via Bathgate
12	St Fergus	Aberdeen
14	Barrington	Kenn South
15	Longtown	Warburton	1984
16	Barrow	Lupton	1983
16	Stapleford Tawney	Stanford Le Hope
17	Theddlethorpe	Hatton	1988
18	Peterborough	Cambridge	1988–94
18	Isle of Grain	Gravesend	2008
18	Matching Green	Rye House
18	Matching Green	Tilbury	1990
18	St Neots	Little Barford
19	Easington	Paull	1991
20	Ilchester	Choakford	1989
21	Mawdesley	Alrewas	1992–2001
21	Carnforth	Burscough	1992
21	Elworth	Deeside power station	1994
22	Goxhill and Hatton	Peterborough	1993
23	Churchover	Honeybourne	1998–2001
23	Peterstow	Gilwern	2000
23	Wormington	Corse	2000
24	St Fergus	Lochside	2001
24	Easington	Paull	2010
24	Hatton	Silk Willoughby	2001
25	Bridge Farm	Mickle Trafford	2001
26	Huntingdon	Steppingley	2001
27	Bacton	King's Lynn	2003
27	Cambridge	Matching Green	2002
28	Herbrandston	Corse	2007
29	Easington	Nether Kellett	2006–08

The NTS now comprises over 7,600 km of welded steel gas pipelines. The Canvey to Leeds line is no longer part of the NTS.