According to the
CAA Website:
We have received a number of enquiries from Non-UK licence holders about exercising the privileges of their licences within the UK. The situation is as follows:
Article 50(i) of the Air Navigation Order 2009 (the ANO), states that a pilot must hold an appropriate licence to fly a UK registered aircraft. An appropriate licence is a licence granted or rendered valid under the Order.
JAA aeroplane and helicopter licences are, subject to the conditions included in it, validated by the Certificate of Validation in the Official Record Series No.4 – Miscellaneous, ORS4 No.747
A licence, except a Student Pilot Licence or equivalent 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 a direction to the contrary. However, Article 62(4) of the ANO states that the holder of such a licence cannot:
1) Act as a member of the fight crew of any aircraft flying for the purpose of commercial air transport, 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 L&TS for advice.
Although the intro states the enquiries regards operating within the UK, nothing I read states it is not applicable outside the UK.
The UK ANO states it is legal to fly a G Reg machine on a valid ICAO license and medical.
I don't know what would stop this being legal crossing the border, unless the respective countries have legislation that states reg and license have to be the same.