A strike by London Underground workers will "definitely go ahead" for 24 hours from Wednesday evening as unions have not been given enough time to study a new pay offer, a senior negotiator has warned.

LU's offer, including an average two per cent rise this year and £2,000 for drivers on the new all-night service, was conditional on unions responding by 6.30pm tonight, so that if the action is called off, plans can be made on running services.

Almost 20,000 workers are due to strike for 24 hours from 6.30pm on Wednesday - Budget Day - in a dispute over the new all-night Tube services.

Transport for London is warning there will be no trains running at all during the walkout.

A message from TfL said: "If this goes ahead, there will be no Tube service from late afternoon on Wednesday 8 July and no Tube service at all on Thursday 9 July.

"All other public transport services and roads would, of course, be much busier than usual.

"We will be issuing detailed travel advice to customers as soon as we can."

The Rail, Maritime and Transport union (RMT), Aslef, Transport Salaried Staffs Association and Unite have been in dispute over pay being offered for the new service, due to start at weekends from mid-September, as well as rosters.

LU's chief operating officer Steve Griffiths said in a message to staff that a "full and final" offer had been made in a bid to conclude five months of talks.

The offer is for an average two per cent increase on basic pay, RPI inflation or one per cent, whichever is greater, in 2016 and 2017, a £500 non consolidated "launch bonus" to all staff on night Tube lines or at stations serving these lines, and a £2,000 "transition bonus" for drivers working on the night Tubes.

Finn Brennan, a senior negotiator for Aslef, ssaid the four unions were not being given enough time to consider the proposed new deal.

Mr Brennan said unions were prepared to return to Acas tomorrow for more talks but were being told the new offer will be off the table by then.

"This is playground negotiating. Having made no offer for three months, they give four unions one afternoon to consider a new offer.

"The strike will definitely go ahead - the company has said the offer is off the table at 6.30pm."

Mr Brennan said the offer was "designed to be divisive" because some workers were being offered more money than others.

The RMT described the offer as "divisive and unacceptable" and the union's executive will be recommended to reject it.

General secretary Mick Cash said: "While a small minority of staff are being offered a non-consolidated one-off lump sum the remainder of staff are ignored and the key issues of work/life balance and the personal health and safety concerns are sidelined.

"The deal as it stands is financed off the back of the proposed axing of over 800 safety-critical station jobs and is deliberately constructed to play individuals off against each other in the most cynical fashion.

"RMT is a democratic organisation and the views of our reps on LU are being taken into account.

"There will be a meeting of the union executive tomorrow morning at which there will be a recommendation to reject the offer. As is normal in all industrial negotiations RMT will remain available for talks."