One of the UK’s biggest casino groups will battle with the National Bank of Abu Dhabi at the High Court on Wednesday over millions in credit extended to high-rolling gambler Ahmed Al-Reyaysa.

Grosvenor Casinos claims that the bank verbally agreed to honour £6.7m ($13.1m) in cheques written by Mr Al-Reyaysa, who patronised upmarket London gaming dens such as the Ritz, Aspinalls and the Clermont Club. During his 18-month membership at the Clermont, which was sold by Grosvenor in 2006, Mr Al-Reyaysa gambled more than £150m.