The 110-plus RMT members involved - who returned a unanimous vote for action earlier this month - will stop work at Waterloo International and North Pole between 14:00 and 17:30 on Friday August 26 and between 07:00 and 10:30 on Saturday August 27, while at Ashford they will strike from 07:00 to 10:30 on Friday and from 07:00 to 10:30 on Saturday.

"Chubb have agreed with us a framework for negotiation, but the problem is that so far they have simply failed to negotiate with us over pay," RMT general secretary Bob Crow said today.

"The depth of our members' anger was made absolutely clear when every single vote cast in our recent ballot was in favour of strike action.

"Our members do a responsible and demanding job and are rewarded with pay levels as low as £6.32 an hour, and even the highest-paid are on less than £7.50.

"We asked the company to make an interim award as a gesture of goodwill to avoid industrial action, but to date they have refused to budge.

"If the company will not use the very bargaining machinery it has just agreed with us we have no option but to move to industrial action, but Chubb know they can avoid strike action by negotiating improved pay rates," Bob Crow said.