Amendment of the Rehabilitation of Offenders Act 1974 (Exceptions) Order 1975
2. The Rehabilitation of Offenders Act 1974 (Exceptions) Order 1975[3] is hereby amended in accordance with the following provisions of this Order.
Amendment of article 3
3. - (1) In article 3(a)(ii) after the word "paragraph" there shall be inserted the words "12 or".
(2) In article 3(b) the words "the Civil Aviation Authority," shall be deleted.
(3) After article 3(b) there shall be inserted:
" (bb) any question asked by or on behalf of
(i) the Civil Aviation Authority,
(ii) any other person authorised to provide air traffic services under section 4 or section 5 of the Transport Act 2000[4] (in any case where such person is a company, an "authorised company"),
(iii) any company which is a subsidiary (within the meaning given by section 736(1) of the Companies Act 1985[5]) of an authorised company, or
(iv) any company of which an authorised company is a subsidiary,
where, in the case of sub-paragraphs (iii) and (iv) of this paragraph the question is put in relation to the provision of air traffic services, and in all cases, where the question is put in order to assess, for the purpose of safeguarding national security, the suitability of the person to whom the question relates or of any other person for any office or employment where the person questioned is informed at the time the question is asked that, by virtue of this Order, spent convictions are to be disclosed for the purpose of safeguarding national security;".
http://www.opsi.gov.uk/cgi-bin/htm_h...er_first_match
so it looks like you will have to declare any spent conviction to an airline if asked. Whether they wiil bother checking spent convictions is another matter.