Mike Ashley, the Newcastle United owner and Sports Direct boss, has won a £14m High Court battle with a former business associate after persuading a judge that a boozy conversation in a London pub had not culminated in a legally binding promise to hand over millions of pounds.

The case centres around a drinking session in January 2013 attended by the billionaire founder of Sports Direct, who was described in court as a “power drinking, money making machine”. Three investment bankers were also present, as was Jeff Blue, a corporate financier who was working for him at the time.

After drinking several pints, Mr Ashley promised to pay Mr Blue £15m if he could double the Sports Direct share price to £8 within three years, the court found.

“But no reasonable person present in the Horse and Groom would have thought that the offer to pay Mr Blue £15m was serious,” said Mr Justice Leggatt, handing down his judgment at the High Court on Wednesday. The agreement was “not a serious discussion…but was banter in which Mr Ashley was displaying his wealth and scale of ambitions”.

The judge continued: “No one who was actually present, including Mr Blue, did in fact think so at the time. They all thought it as a joke. The fact that Mr Blue has since convinced himself that the offer was a serious one shows only that the human capacity for wishful thinking knows few bounds.”

During his testimony, Mr Ashley denounced Mr Blue, a former Merrill Lynch banker, as a “total liar”, and said the lawsuit was an example of how, “because I am successful, some people try to take advantage of me”.

The judge said that they were “mischievous allegations that had no relevance to the case and ought not to have been included”, but said that he did not think it was right to award indemnity costs in this case. Instead Mr Blue will face initial legal costs of £600,000 which must be paid within 21 days.

Mr Blue was suing for £14m because he said £1m under the purported deal had already been paid.