That old FAA to JAA question again..

[BHenderson]

You don't need to convert in order to self fly hire in the UK. (This doesn't apply if you then go abroad.) In fact it would be more of a pain to convert. The licence is automatically valid - no paperwork. Make sure you have your radio licences for your FAA/TC licences though.

(4) For the purposes of this Part of this Order:
(a) subject to sub-paragraph (b), a licence granted either under the law of a Contracting State other than the United Kingdom but which is not a JAA licence or a licence granted under the law of a relevant overseas territory, purporting in either case to authorise the holder to act as a member of the flight crew of an aircraft, not being a licence purporting to authorise him to act as a student pilot only, shall, unless the CAA gives a direction to the contrary, be deemed to be a licence rendered valid under this Order but does not entitle the holder:
(i) to act as a member of the flight crew of any aircraft flying for the purpose of public transport or aerial work or on any flight in respect of which he receives remuneration for his services as a member of the flight crew; or
(ii) in the case of a pilot's licence, to act as pilot of any aircraft flying in
controlled airspace in circumstances requiring compliance with the
Instrument Flight Rules or to give any instruction in flying;

Ref: http://www.caa.co.uk/docs/33/CAP393.PDF (Page 53)

Bobby