High Court judge reserved judgement on the case brought by industry body, the British Casino Association.
The BCA argues that the plans for a 5,000 square metre supercasino and 16 other large casinos puts the UK's existing crop of casinos at a disadvantage. The High Court verdict is now expected in two to four weeks.
The BCA appeal centres on the government's decision to allow the new batch of casinos to have far more and highly lucrative slot machines than existing venues.
If the High Court judge agrees with the BCA, it would be another setback for the ruling Labour government after its plans were narrowly rejected by Britain's senior lawmakers in March.