LONG queues at the UK's busiest airport have been caused by a lack of effective planning amid job cuts, with border staff signing off at the start of busy periods, inspectors said.

Limited resources are not matched to the demand at London's Heathrow Airport, damaging the ability of staff to maintain effective controls, the chief inspector of borders and immigration John Vine said.

The introduction of a series of significant changes "was simply far too much organisational change during the busiest time of the year", inspectors warned.

The critical report on the UK Border Agency and the Border Force comes as Heathrow faces another shake-up.

Home Secretary Theresa May is responding to the ongoing row over queues in which passengers have been forced to wait up to three hours.

The introduction of new team structures, rosters and shift patterns came as border staff numbers at Terminal 3 fell by 15% from 322 to 277 in the 12 months to last August.

Immigration Minister Damian Green said: "We now have more staff at the border during peak times, greater flexibility to man immigration and customs controls and clearer guidance for staff on when vital checks are required."