Copenhagen Tunnel

Construction and opening

The Copenhagen Tunnel was the last section of the line into London to have its contract issued. To the north was Thomas Brassey's contract,^[4] and to the south was John Jay's contract for the temporary station at Maiden Lane. The contract was awarded to the London-based duo Pearce and Smith who started work on 27 March 1849.^[5] The name is taken from Copenhagen Fields, which were the gardens of the Danish Ambassador in the 17th century.^[6] The fields are notable for being the site of frequent protesting, including against the conviction of the Tolpuddle Martyrs, with the government forced to release them.^[7]

Pearce and Smith were the largest buyers of lime by far in 1849, and it is possible that this was used for the Copenhagen Tunnel. The construction of the tunnel attracted great interest from locals who came to watch the bricks being made.^[5] Pearce and Smith were contracted to build the tunnel, and made the bricks on site using the spoil from digging the tunnel bore, by means of innovative techniques that were new in London at the time. Their first attempt involved using clay and sand but not any ash, which led to hard but brittle bricks that cracked in the kiln. Their improved method involved processing the clay immediately after it was dug out before slop-moulding it into shape having been combined with ash. Many of the bricks have an uneven shape as they were used quickly after they came out the kiln.^[5][8]

The kilns that the bricks were burnt in were coal-fuelled and exposed, which led the bricks to have an unusually red colour but did not affect their efficacy. To save money, Pearce and Smith also sometimes used sawdust rather than sand which was supplied by a sawmill. They also used a single steam engine to power the mortar mill, lifts in the tunnel shafts, and the sawmill.^[8]

19th century

The tunnel was immediately to the north, and part of, the complicated and vast King's Cross Goods Yard and similar surrounding yards which also served the London, Midland and Scottish Railway out of St Pancras and the North London line. Copenhagen Junction and Goods and Mineral Junction were situated just to the south of the tunnel. Much of this infrastructure was not actually visible to passenger trains on the main line, and it required the cooperation of multiple closely-packed signal boxes on both sides of the tunnel. The Metropolitan Cattle Market and its abattoir were situated to the west of the main line and served by their own sidings which were accessed by the goods lines. There were also both the Islington Electric Light Works and the Star Brush Works nearby.^[9]

This area also held the former Great Northern Cemetery Station which was used to transport coffins from London to New Southgate Cemetery for burial.^[9] There was an additional spur that ran perpendicular to the main line and then over the top of the Copenhagen Tunnel to serve the Caledonian Road coal yard, which closed in October 1967. This ran parallel to the North London line, which passes over the ECML just to the south of the southern tunnel bores.^[9]

The lines between the westernmost bore of the Gasworks Tunnel and Copenhagen Tunnel, which are now the Down Slow and Up Slow lines, were formerly the main access lines for the King's Cross Goods Yard and the South London Goods lines. The Holloway Flyover was originally designed to carry the Up Goods into the goods yard, but is now used to carry the Up Slow line into London King's Cross and the canal tunnels.^{[9][1]: 200–201}

20th century

It was at Copenhagen Tunnel where passenger services from King's Cross via the Gasworks Tunnel met goods trains and coal trains from expansive depots situated north of the Regent's Canal.^[3] The western tracks north of the tunnel also had a former connection to the lines serving King's Cross Goods Yard, which connected at Goods and Mineral Junction and its corresponding signal box. The two lines in the Western bore were formerly named the Up Goods and Down Goods for this reason, and also because all three bores were still in situ.^[9]

v t e Copenhagen and Gasworks Tunnels
Legend
to Finsbury Park Fast lines Slow lines Copenhagen Tunnel Copenhagen Junction to North London line to High Speed 1 to Canal Tunnels via Canal Tunnel Junction Regent's Canal Gasworks Tunnel to London King's Cross

The original tunnel is now the middle of three parallel bores. A second tunnel to the west was built in 1877 and a third one to the east in 1886. The western bore carried up and down goods traffic, the central one was used for down passenger traffic and the eastern bore was used for up passenger traffic. Following electrification in the 1970s, the layout was remodelled. This was helped by the fact that King's Cross Goods Yard and Top Shed had closed, so it was possible to remove the goods lines. The eastern tunnel was taken out of railway service but maintained to ensure the integrity of the ground overhead – it provides road vehicle access to Holloway Bank.^[10]

The 1955 British comedy film The Ladykillers is set in the area around King's Cross and St Pancras railway stations and their old goods yards.^[11] One of the sets for the house of the protagonist, Mrs Wilberforce, was built perpendicular to the end of Frederica Street, which sat close to the south portal of the Copenhagen Tunnel. Immediately to the south of the set was the spur which carried a track above the tunnel to the goods and coal yard. In one scene from the film the characters dump others' dead bodies over the south portal of the tunnel onto the tracks below.^[11][12][13] None of Frederica Street, the set, the coal and goods yard, and the spur of track survive today.^[10][11][12]

21st century

On 15 October 2006, a worker lost control of a road–rail vehicle near London King's Cross and it ran away for 1,600 feet (490 m), coming to a stop 100 feet (30 m) into the tunnel. The gradient on the relevant section of track was 1 in 55 (18.2 ‰) and this meant that the vehicle had no effective ability to brake on the rails. The incident was attributed primarily, however, to human error, and the Rail Accident Investigation Branch decided not to pursue a full investigation as the contractor was already working on improving training.^[14][15]

In January 2024, the Copenhagen Tunnel and the neighbouring Gasworks Tunnel became the first in the country to have new signal-boosting technology fitted inside. This stops devices from losing signal and allows passengers to continue calls while travelling through the tunnels. The upgrade was funded entirely by London North Eastern Railway.^[16] As of March 2026^[update], the operators passing through the Copenhagen Tunnel include Grand Central, Great Northern and Thameslink, Hull Trains, London North Eastern Railway, and Lumo.^[17]