The Hammersmith and City line carries 55,000 people a day

But Chris Barrett said it was the only way he could try to get his �32,000-a-year job back and support his family.

He was suspended after playing squash while off sick with an ankle injury, but says it was part of his recovery process.

Two strikes will be held on Christmas Eve and New Year's Eve to support him.

He told London's Evening Standard: "I'm really sorry if by having a strike I'm going to ruin people's Christmas but my whole life has been ruined.

"I don't want revenge, I just want my job back."

Appeals process 'exhausted'

The row has already led to one strike, in November, which closed the Circle line and meant LU could only run a shuttle service on the Hammersmith and City line.

The Rail, Maritime and Transport (RMT) union said Mr Barrett was sacked unfairly and wants him to be re-instated.

General Secretary Bob Crow has said the union was prepared to hold talks at the conciliation service Acas.

But LU says Mr Barrett has "exhausted the appeals process".

Among critics of the strike is London mayor Ken Livingstone, who pointed out Mr Barrett had taken 218 days off sick in five years.

The RMT says drivers will not clock on for shifts starting between 0430 GMT on 24 December and 0429 GMT on 25 December, and between noon on 31 December and 1159 GMT on 1 January, 2004.