A “novice” trader who made £10m profit while “practising” has launched legal action against a British firm after it refused to let him keep the money.

Harouna Traoré is suing UK-based Valbury Capital after it seized the earnings he made while using what he believed was a demonstration version of its platform.

The day trader opened a £20,000 account with the company last summer after using a simulation of its trading software to practice dealing in equity futures, according to The Financial Times.

A couple of weeks into the training course, Traoré placed a £1bn order for securities, before realising he was on the live platform and had accumulated a loss of over £1m.

In a bid to recoup his losses, he carried on trading, turning his debt into a profit of more than £10m and building up a $5bn position in US stock futures.

Despite an impressive turnaround, Valbury claimed that Traoré was in breach of his contract and that his holdings were “void and cancelled”.