Thousands of London Underground workers have been offered a payment of £850 each for working during the 2012 London Olympic Games, it has been revealed.

The Rail Maritime and Transport union had declared a dispute with London Underground after the lack of progress over an Olympic payment. However there have been talks this week at the conciliation service Acas.

The union said it had received an offer of £850 for all Tube staff, adding it would affect up to 18,000 workers.

General secretary Bob Crow said: "Clearly moving from offering nothing to the latest offer of £850 is a massive shift on the part of London Underground.

"The offer will now be considered by our reps and by the full executive before we make a formal response."

The union had rejected previous offers, saying there were too many strings attached to proposed deals.

The RMT has struck several deals with rail companies for extra pay during the London Games this summer, including a bonus of £500 for staff at Virgin Trains and Network Rail, £600 for London Overground workers and an agreement with Docklands Light Railway which union officials said could be worth up to £2,500.

The union is balloting hundreds of administrative staff it represents at Transport for London (TfL) for industrial action over "severely restricted" annual leave during the Games.

Officials claimed that leave had been banned altogether for the duration of the London 2012 Olympic Games in one department, saying this would make life "impossible" for many staff, especially those with school-age children.

The RMT also announced it will ballot workers at Tube Lines for industrial action in a row over pensions and travel passes.

The union said it wanted employees at Tube Lines, now a subsidiary of TfL, to be able to join the company's pension scheme and receive the same travel concessions as other staff.

Howard Collins, LU's chief operating officer, said: "We have had productive discussions with the unions this week and put forward our proposals about how we can fairly reward staff.

"We have put forward an offer which would see station, maintenance, service control staff and operational managers receive up to £850 for working flexibly during the 2012 London Games, subject to attendance, customer satisfaction scores and agreement from operational staff to work flexibly in order to deliver a successful Games.

"In return we are asking staff to work longer hours at different times of the day, to be prepared to work extra hours and to be more flexible in how and where they carry our their role for us during these crucial weeks. We know our employees want to play their part in delivering a great games for London, so reaching agreement on this will allow all of us to focus on that exciting challenge together."

Lee Jones, operations director for Tube Lines, said: "We have been discussing this issue with our trade unions for some time, and we will continue to try to find a way forward through constructive discussion. We would urge the RMT to withdraw its threat of a strike ballot, which will not achieve anything."