Treasury officials "forgot" that tour operators could not impose surcharges on booked holidaymakers, and so saddled the industry with an unfair and unlawful £50m burden when air passenger duty was doubled in February, a High Court judge was told yesterday.

The claim came as the Federation of Tour operators began a legal challenge to the levy's increase, which was vaunted by Gordon Brown, then chancellor, as a "green tax" in last year's pre-Budget report.