Tube trains will run throughout the night at weekends, London Underground has announced – but most tube ticket offices will go and 750 jobs will be lost.

From 2015 trains will run on Friday and Saturday nights on core parts of the tube network, as part of a package of measures for a "21st-century tube service", including direct payment by bank cards. But unions and Labour hit out at moves to close ticket offices and cut jobs.

London Underground says the move to redeploy staff will make them "available to give the best personal and face-to-face service to customers". According to Transport for London (TfL), fewer than 3% of tube journeys start with passengers visiting a ticket office.

After redeployment, around 750 jobs will be lost with ticket office closures, LU said, although it promised no compulsory redundancies. The plans will save TfL £270m over five years and it said it was talking to online retailers about converting ticket offices to "drop-off" or "click-and-collect" points for their goods.

Unions promised to fight the cuts and accused TfL and Boris Johnson, the London mayor, of trying to hide the news of cuts. Bob Crow, of the RMT, said the 24-hour train plan was "just a smokescreen to try and camouflage the real issue which is a savage cuts to jobs, access and safety".

Manuel Cortes, leader of the TSSA rail union, said: "It beggars belief that the mayor who was elected in 2008 on a pledge to keep open every ticket office is now planning to close every single one, with all that means for safety and jobs."

The shadow London minister, Sadiq Khan, said there were serious concerns about whether there would be enough staff to respond in emergency situations. He said: "We support looking at the way TfL staff work so that it reflects the changing needs of the modern underground system, but the mayor is using this as an excuse to cut staffing levels, which is reckless and irresponsible."

However Boris Johnson, the London mayor, said the plans were not against London Underground's staff interests, and in the long-term the tube "eventually will need more staff". He confirmed that drivers could be axed, saying: "Whether you will need more old-fashioned drivers in the train is doubtful."

He said he hoped unions and public would support his plans, which were effectively expanding the tube and driven by changes in technology. "What we're doing is getting the tube staff out from behind the plate glass and getting out there helping all kinds of passengers. There will be more staff but there won't be ticket offices because they are no longer relevant," he said.

The weekend "night tube" service will start on the Piccadilly, Victoria, Central and Jubilee lines, as well as key sections of the Northern line, from 2015. All stations will be staffed while services operate. The network, which should be expanded to other lines in future, is planned to dovetail with night buses for integrated services through the night.

Mike Brown, managing director of London Underground, said: "Rebuilt stations, new trains and signalling systems mean we are now running some of the most frequent metro services anywhere in Europe. To meet the challenge of London's growing population and development, we must continue to invest and deliver even more efficiently in future.

"Our vision is for a tube network and service that is truly fit for London and our customers in the 21st century – a better face-to-face service at our stations, a 24-hour service at weekends, with easier and more personalised ways to plan and pay for journeys, on and off our network."

Johnson added: "For 150 years the tube has been the beating heart of London, its tunnels and tracks providing the arteries that have transported millions of people and helped to drive the development and economic growth of our great city.

"Now it is time to take the tube to the next level and so for the first time in London's history we will provide a regular 24-hour night tube service at weekends. This will not just boost jobs and our vibrant night-time economy, it will further cement London's reputation as the best big city on the planet to in which to live, work, visit and invest."

Johnson said trains would run throughout the night at "thrilling frequency" – or every 15 minutes. "Passengers will be fighting them off with a stick," he said.

Additional improvements will include more frequent daytime trains on some of the busiest lines, with a 20% increase in capacity on the Northern line next year.

The process of phasing out current ticketing will start as transactions move to direct payments, with entry via contactless bank cards starting next year. Brown said that Oyster cards would stay in use as long as customers wanted them. Better access to stations and trains for disabled customers is promised. Wi-Fi coverage will be extended to virtually all below-ground tube stations by the end of 2014.