Mike Ashley, the Newcastle United owner and Sports Direct boss, has won a High Court battle with an investment banker over a £15 million deal allegedly made in a London pub.

The case revolved on an evening of "heavy drinking" in 2013 where Jeffrey Blue, a former investment banker, claimed that the billionaire agreed to pay him £15m if he helped Sports Direct's shares to rise from £4 to £8.

A judge this morning dismissed the £15m claim after declaring that an agreement was "not a serious discussion...but was banter in which Mr Ashley was displaying his wealth and scale of ambitions".

Mr Justice Leggatt said that the "jocular" remark by Mr Ashley that he would pay Mr Blue was not a contract and "that there was no one present in the Horse & Groom pub who thought that it was genuine...they all thought that it was a joke."

The judge said in summary "the fact that Mr Blue has since convinced himself that the offer was a serious one, and that a legally binding agreement was made, shows only that the human capacity for wishful thinking knows few bounds.

Mr Ashley's legal team, led by David Cavender QC, attempted to pursue Mr Blue for £1.5m in legal costs and indemnity, after arguing that a number of allegations made by Mr Blue's witness statement were irrelevant to the case and designed to embarrass Mr Ashley and put pressure on him to settle.