Unite claims that the bank has told employees that 40% of permanent staff - 650 people - from its London IT function will be let go over the next three years. In addition, a 65% reduction in contractors will see another 230 people lose their jobs.

In 2016 majority state-owned RBS employed 2200 IT staff in London but by 2020 there will be just 950 full timers.

Rob MacGregor, Unite national officer, says: "By 2020 just a fraction of the RBS IT function will remain, leaving this organisation operating a skeleton service with the customers and remaining staff paying the price.

"RBS’s fixation with cutting employee numbers, restructuring and offshoring work that could reasonably be done by displaced staff within the RBS IT community is unacceptable. This British-taxpayer funded bank should be concentrating on investing in jobs here in the UK, rather than wholesale cuts."

The news comes just three months after the the bank outlined plans to cut hundreds of UK tech jobs, offshoring some of the work to India.

A bank spokesperson says: "Inevitably as RBS becomes a simpler, smaller bank focused on the UK and Ireland, our technology function will undergo reorganisation and will reduce over time. As we develop long-term plans for our technology business, we have, in the interests of transparency, started to share our emerging proposals on a future operating model with Unite.

"We have not consulted on any headcount reduction, instead sharing a direction of travel with Unite which is subject to change. Our proposed plans are designed to reduce the number of contractors we employ and strengthen our permanent workforce and while we are downsizing in London we are reinvesting in other UK hubs."