[holding answer 6 May 2008]: The EU airport slot allocation regulations require airlines to use their slots for 80 per cent. of the time or return them to be re-allocated to other airlines by the independent slot co-ordinator. The UK independent slot co-ordinator is not aware of any cases at present where an airline is flying empty aircraft to retain an airport slot. Such cases are very rare, the cost of fuel being a disincentive. Hence we have not made an assessment of the environmental impact.