This link (on the CAA website)
http://www.caa.co.uk/default.aspx?ca...=170&faqid=208 will get you...
Exercising the privileges of a JAA Licence or an ICAO licence in UK Registered Aircraft
We have received a number of enquiries from Non-UK licence holders about the privileges of their licence within the UK. The situation is as follows:-
Article 21, of the Air Navigation Order 2000, states, that a pilot must hold an appropriate licence granted either by the UK CAA or by a foreign authority and rendered valid under the ANO to fly a UK registered aircraft.
A JAA licence is deemed to be a licence rendered valid under the ANO unless the CAA in the particular case gives a direction to the contrary. A JAA licence is a licence issued in accordance with licensing and medical requirements of JAR-FCL by a full JAA Member State that has been recommended for mutual recognition by Central JAA (JAA Headquarters). For the current mutual recognition status of
JAA Member States please select this link.
A licence issued by any other ICAO Contracting State (including a JAA State that has not yet been recommended for mutual recognition) is also deemed to be valid under the ANO for the purposes of flying a UK registered aircraft, providing that the licence and medical are valid in accordance with the rules/laws of the issuing State, and the CAA does not in the particular case give direction to the contrary. However, Article 21 (4) (a) states that the holder of such a licence cannot:
1) 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
2) In the case of a pilot’s licence, act as a pilot of any aircraft flying in controlled airspace in circumstances requiring compliance with the Instrument Flight Rules or to give any instruction in flying.
Where a licence contains any extraordinary operational or medical limitations, individuals should contact PLD for advice.
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So a current (flight review within last two years, sufficient take offs/landings for passenger carrying, etc) FAA licence with a current FAA medical is sufficient.