Llay Main Colliery

Overview

Llay Main was the most ambitious thing ever attempted on the Denbighshire coalfield. Llay Main Collieries Ltd. began sinking two shafts in 1914 to reach coal nobody had been able to work before; the Home Office stopped the work in 1917 and it did not finish until April 1921, with first coal in 1923. At 905 yards the No. 1 shaft was among the deepest in Europe, and after nationalisation both shafts were deepened to 1,000 yards, making Llay Main the deepest pit in Britain. It became the largest colliery in Wales, employing over 3,000 men, and a whole village was built to house them. Nine men and boys were killed by an explosion in 1924 (see Disasters, below). Geological difficulties and falling output closed the pit in 1966.

History

Sinking began in 1914 and was suspended by order of the Home Office in 1917, wartime resources being needed elsewhere. It restarted in January 1919 and was completed in April 1921; the first coal came up in 1923, nine years after the first sod. The scale of the undertaking was such that a new village had to be built at Llay for the workforce, and it remains the reason the place exists in its present form. By 1923 the colliery employed 2,013 men. In 1929 it was raising nearly 4,000 tons a day, and its record year produced 1,057,592 tons — over a million tons from a single pit, which no other Welsh colliery matched. Peak employment passed 3,000, making it the largest colliery in Wales. Llay Main Collieries Ltd. sold out to Charlton Main Colliery Ltd. in 1926, and the pit passed to the National Coal Board at nationalisation in 1947. On 5 December 1924, an explosion in the North Two Yard district killed nine men and boys. The divisional inspector’s report to Parliament was sharply critical of how the district was ventilated (see Disasters, below).

Geology

Llay Main worked the Denbighshire coalfield, the northern continuation of the same Carboniferous Coal Measures worked around Wrexham. The seams taken were the Two Yard, the Brassey and the Main, yielding both house and steam coal. What made the colliery exceptional was depth rather than the coal itself: the measures here lie under a great thickness of overlying strata, and reaching them at all required shafts far deeper than anything else in the district — which is exactly why the reserves had been left alone until a company was willing to spend seven years sinking to them.

Geological setting: Sedimentary Beds and Seams (well documented example)

Workings

Two shafts served the colliery, No. 1 the downcast and No. 2 the upcast, sunk to 905 and 810 yards respectively with winding depths of 776 yards each. After nationalisation both were deepened to 1,000 yards. In the workings, ventilation of the outlying districts partly depended on exhaust air from a haulage engine — an arrangement the inspector who investigated the 1924 explosion condemned, along with the shortage of brattice cloths that let air short-circuit before reaching the high side of the face. Abandonment plans for Llay Main are catalogued at the British Geological Survey’s Keyworth store.

Closure

Llay Main’s workforce was cut back in 1959 and the pit closed in 1966, its annual output down to 240,767 tons — under a quarter of what it had raised in its record year. Geological difficulties are given as the reason. Filling the two shafts took six months and 60,000 tons of mine waste.

What remains

Nothing of the colliery survives. Llay Industrial Estate was built over the site, and the shafts are somewhere beneath it, filled with the pit’s own spoil. The street names — Miners Road, Miners Park — are what is left of the naming.

A pithead winding wheel was installed at Llay in 2012 as a permanent memorial to the men who worked the colliery. Beyond that the village itself is the monument: Llay was built for the pit, and its layout and housing are a direct product of the 1920s sinking.

Abandoned workings can be dangerous — unstable ground, uncapped shafts, flooding and bad air are common even where a site looks safe from the surface. This entry describes history and general location only; it is not an access guide.

Disasters & major incidents

• Llay Main Colliery Explosion
  5 December 1924 · Explosion · 9 fatalities
  At about a quarter past one on the morning of Friday 5 December 1924, gas ignited in the North Two Yard district of Llay Main Colliery, near Wrexham. The flame travelled only twenty or thirty yards, but nine men and boys died in it — including the fireman who had fired the shot that set it off. The other 407 men underground got out. The divisional inspector’s report to Parliament found the district’s ventilation inadequate and criticised the practice of relying on exhaust air from a haulage engine to ventilate working places.

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• Sinking began in 1914, was suspended by Home Office order in 1917, resumed in January 1919 and was completed in April 1921; the first coal was drawn in 1923. ^1,2
• No. 1 (downcast) and No. 2 (upcast) were sunk to 905 and 810 yards, with winding depths of 776 yards each. ¹
• After nationalisation both shafts were deepened to 1,000 yards, making Llay Main the deepest pit in the country. ¹
• At sinking the colliery was described as the deepest pit in Europe, at a depth of about 730 metres. (disputed) ²
• The record year produced 1,057,592 tons; by 1929 the pit was raising nearly 4,000 tons a day. ¹
• Employment was 2,013 men in 1923 and 2,501 in 1945, passing 3,000 at its peak — the largest colliery in Wales. ¹
• The colliery closed in 1966 because of geological problems, output having fallen to 240,767 tons a year. ¹
• Filling the two shafts took six months and 60,000 tons of mine waste. ^1,2
• A pithead winding wheel was installed at Llay in 2012 as a memorial to those who worked the colliery. ²
• Abandonment plans for Llay Main are catalogued in the BGS mine plans collection at Keyworth. ³

Photographs & further reading

This page doesn't try to reproduce everything — these are the best original sources found for this mine.

Sources

1. (secondary) Llay Main and Llay Hall collieries, Wrexham — Welsh Coal Mines
2. (primary) 1924 — a significant year in Llay village history — Royal Commission on the Ancient and Historical Monuments of Wales
3. (primary) BGS mine plans catalogue: LLAY MAIN — British Geological Survey
4. (secondary) Llay Main Colliery Explosion, Wrexham, 1924 — Northern Mine Research Society

Record created: 26 August 2026 · Last researched: 26 August 2026