The £5m gift to Nigel Farage by a cryptocurrency billionaire was reported to the National Crime Agency by bankers who were concerned it may have been laundered money, the Guardian can reveal.

The disclosure will put further pressure on the Reform UK leader, who is awaiting a decision by the standards commissioner over whether his failure to declare the money breached parliamentary rules.

Farage was given a deadline of 1pm on Tuesday to respond to the Guardian about this article. He gave a video address at 2pm announcing he would force a byelection in his seat of Clacton-on-Sea.

That attempt to shake off the deepening scandal over his finances appeared to have backfired on Tuesday night as the Conservatives, Labour, Restore Britain and the Lib Dems all announced that they would not stand candidates in a contest described as a “media circus” and “vanity project”.