Twitter co-founder Biz Stone has joined the board of British financial technology firm R8 as it prepares for a listing on the London Stock Exchange in this summer.

Stone, who recently returned to Twitter to work alongside co-founder Jack Dorsey, will invest as part of £4m of new funding in R8.

Founded by Jonathan Rowland, son of major Tory party donor David Rowland, R8 controls a group of technology start-ups, including cryptocurrency company Mode and electronic payments company Jgoo.

R8 is aiming to go public later this year with plans to raise around £20m at a valuation of up to £50m.

Twitter's Stone has been a notable early stage investor in a number of US start-ups, including payments company Square and workplace messaging company Slack.

R8 has kept its plans out of the public eye, but has described its plans to develop "a large fintech project with a very ambitious goal... to build the first fully regulated, crypto-friendly bank in the UK".

R8 was spun out of challenger bank Redwood Bank. Founded in 2015, Redwood Bank began as "a niche business bank focused to lending to SMEs and very simple deposit products," Rowland said.