London retailers are braced for a further blow to sales this Christmas after Tube drivers voted in favour of a walkout on Boxing Day.

Retailers in the West End could find sales impacted by between 20% and 30% on December 26, the first day of the key post-Christmas Sales, after London Underground drivers voted 9 to 1 in favour of industrial action.

Boxing Day is a crucial trading day for retailers, which are already trying to claw back sales lost to the snowy weather in recent weeks. Last year about £120m went through West End retailers’ tills on Boxing Day.

A Transport for London spokesman told the BBC: “It is disgraceful that [union] Aslef should try to hold Londoners and London Underground to ransom in this way.”

London Underground had told workers that December 26 was a normal working day for drivers but unions want members to have triple pay and a day off in lieu for working on the day.

Retailers in the capital have been disrupted by a string of strikes over pay and working conditions in recent months.