Unless my reading of Schedule 11 of the ANO is incorrect (
http://www.legislation.hmso.gov.uk/s...1562.htm#sch11) there is no requirement for a pilot on a private flight in the UK to carry an identity document (other than a licence). Whilst I agree that it is sensible to carry something I don't see how the airfield has any legal authority to demand photo ID (any more than my local rail station has).