• UPDATE: Aslef says the strike will 'definitely go ahead'
• London Underground workers strike dispute over Night Tube
• Up to 20,000 staff to walk out on Wednesday afternoon
• Strike to cause problems for Wimbledon spectators
• FGW strike to affect Ashes Test cricket fans travelling to Cardiff
The strike, which could see a walk-out by almost 20,000 workers, is scheduled to begin on Wednesday evening and is part of a dispute over the new all-night service which is set to operate across the capital from September.
The Rail, Maritime and Transport union (RMT), Aslef, Transport Salaried Staffs Association (TSSA) and Unite are unhappy over pay being offered for the new service, as well as rosters.
Talks were held at the conciliation service Acas last week without any sign of progress and both sides met again on Monday. By 3.30pm a spokesman for Aslef said the strike will "definitely go ahead" because unions have not been given enough time to study a new pay offer.
If all four unions walk out, there will be no Tube service from late afternoon on Wednesday 8 July and none at all on Thursday 9 July.
Online literature for Transport for London, which runs the London Underground, advises: "All other public transport services and roads will be much busier than usual, so please check before you travel."
Finn Brennan, chief negotiator for Aslef, told The Independent it would be the biggest strike since 2002.
He said: “We are anticipating it will be a complete shut-down of the entire underground system.”
#Breaking Talks aimed at averting a 48-hour strike by workers on First Great Western from Wednesday evening have broken down— Press Association (@PA) July 6, 2015
Members of the RMT, Unite and TSSA are planning a 24-hour strike from 18.30 on Wednesday 8 July, while Aslef drivers are planning the same on the Tube from 21.30.
DLR, London Overground and Tfl Rail staff will not be striking.
On Monday it also emerged talks aimed at averting a 48-hour strike by workers on First Great Western (FGW) due to start on Wednesday evening had broken down.
The action, over jobs and maintenance of new Hitachi trains, will affect services between London and Wales and the West Country.
Cricket fans going to Cardiff for the Ashes Test are among those affected.
The union accused FGW of "playing for time" in the talks and of "going through the motions" rather than addressing the issues.
The RMT said it is campaigning to avoid job losses, keep a safety-competent guard on every train, maintain buffet car facilities and ensure that the maintenance of new rolling stock remains in-house.
General secretary Mick Cash said: "RMT has made every effort to secure a series of very basic assurances from FGW over jobs, services and safety as a result of the introduction of the new Hitachi fleet and they have shown no intention of addressing those issues in the talks today.
"RMT is angry and disappointed that the company have ignored the massive vote for action by their staff and have instead opted to plough ahead with a series of actions that will decimate jobs, services and safety. As a result of FGW collapsing the talks in this cavalier fashion the action goes ahead as planned.
"It is frankly ludicrous that East Coast, who are introducing the same trains, have given us the assurances we are seeking but FGW have ignored us and are crashing on with the ripping out of buffet cars and the threat to safety-critical station and train staff purely to maximise the profits from new trains bought for them by the British taxpayer.
"RMT will be out at stations this week with a public campaign to expose this shabby and profiteering treatment of both passengers and staff alike by a company that already has one of the worst reputations in the industry for milking the rotten rail privatisation racket for every penny they can."
An FGW spokesman said: "All we want is to make sure our services give the best possible deal for our passengers. These brand new trains have been designed to deliver more seats, and faster, more frequent journeys for passengers - but we can't deliver those if they are operated in the same way as the 40-year-old trains that run today.
"We have already made assurances about job security and commitments to increase the number of staff on board Super Express Trains.
"Today we have made a number of additional commitments that we believe meet the concerns of the RMT, while still allowing us to deliver the improvements our customers want to see.
"While it is disappointing that the RMT were not able to take this proposal away today, we believe a negotiated solution to these proposals is possible, and are keen to continue discussions as soon as possible."