UK Coal was under more pressure yesterday after it emerged it is unable to meet a contract to supply the UK's largest coal-fired power station.

The mining group blamed geological problems at its Kellingley colliery for a shortfall with the nearby North Yorkshire power station Drax.

The problems come only eight months after UK Coal announced a deal to supply Drax with about 18 million tonnes of coal over a five-year period.

Drax said it had been told to expect a shortfall of 750,000 tonnes in the year to March, while there may be a gap of 500,000 tonnes in each year up to 2009.

The power station said it was confident that its remaining requirements could be met by other coal producers.

The business pledged to seek recovery of additional costs from UK Coal although, in the meantime, the situation would knock £10m off this year's earnings and up to £5m from next year's.

Shares in UK Coal, which last week announced plans to close its Welbeck Colliery, at Mansfield, Nottinghamshire, fell by nearly nine per cent.

The company said in January that unforeseen geological problems had affected plans for the Kellingley colliery. As a result, it cut its production target and reduced the workforce of 700 by 180.

Drax is close to the Selby complex closed by UK Coal last year.

The National Union of Mineworkers called on the Government to step in to end the "charade" of pits being closed while supply problems existed.

President Ian Lavery said it was "absolutely scandalous" that UK Coal was closing pits but could now not meet its contract to supply coal.

Drax, which has estimated its annual coal requirement at about 10 million tonnes, also takes supplies from up to 15 other companies.

In November, UK Coal reported a fall in sales volumes for the previous four months and said its deep mining operations - at eight sites after the closure of the Selby complex - had been disappointing.

Long-term contracts mean UK Coal has yet to take advantage of a 40 per cent year-on-year improvement in worldwide coal prices.