Former Rangers shareholder and sportswear firm boss Mike Ashley would lie under tables and "take a nap" at meetings he found boring, a finance expert embroiled in a High Court fight with the businessman has told a judge.

Investment banker Jeffrey Blue has sued Mr Ashley after claiming the Sports Direct boss did not stick to a commercial agreement.

Mr Ashley disputes the claim.

Mr Justice Leggatt began analysing evidence at a High Court hearing in London on Monday.

Barrister Jeffrey Chapman QC, who is leading Mr Blue's legal team, told the judge Mr Ashley's business practices flew in the face of "business orthodoxy".

He said Mr Blue referred to Mr Ashley lying underneath tables at "boring" meetings and "playing a game of spoof" to decide who paid an investment bank's fees.

The judge had heard the dispute between Mr Blue and Mr Ashley related to an alleged conversation in a London pub in 2013.

Mr Blue says Mr Ashley made a promise during a meeting in a pub called the Horse & Groom.

He says Mr Ashley promised to pay him £15 million if he used his expertise to increase Sports Direct's share price to £8 a share.

He says Mr Ashley paid only £1 million.

"Mr Ashley's business practices fly in the face of business orthodoxy," Mr Chapman told the judge in a written outline of Mr Blue's case.

"Mr Blue refers to Mr Ashley lying underneath tables in meetings he found to be boring to 'take a nap', playing a game of spoof to resolve who ought to pay Merrill Lynch's legal fees ... (totalling £750,000) and lavishly entertaining Sports Direct's non-executive directors."

Mr Chapman said the judge would have to consider the relevance of the fact that the discussion took place in a pub.

He added: "Mr Ashley is not an ordinary businessman, does not conduct business in an orthodox way or in business-like environments."