I have a licence issued by a non-EASA country (e.g. USA), how will the changes affect me?
Currently the UK Air Navigation Order gives a permanent validation of non-UK ICAO licences that allows the holders of those licences to fly UK-registered aircraft for private purposes only. With the implementation of European regulations, including the use of the derogations by the UK, this UK validation will remain for private flights until 8th April 2014. From that date forward the UK validation will be valid only for non-EASA aircraft registered in the UK.
For any commercial flight in a UK-registered aircraft, the holder of a licence that is not a UK or JAR licence must hold an individual validation issued by the CAA.
Under European regulations there is no general validation for private flying. An individual validation will be required in every case. However, the rules will include a two-year transition period for private flying. This means that from 8th April 2014 onwards, the holder of a licence from a non-EASA State must hold an individual validation certificate issued by the EASA Member State where the pilot or the “operator” of the aircraft is based, if the aircraft is to be flown for any purpose. For any commercial flight where application for validation is to be made to the UK CAA, an individual validation in accordance with the Aircrew Regulation is required from 1st July 2012. Before that date a validation issued under the Air Navigation Order is required, but will be valid for UK-registered aircraft only.
There are some other significant changes to the validation rules being introduced under EU regulations:
Under current national provisions a validation (general or specific) is required for a non-UK or non-JAR licence holder to fly a UK-registered aircraft. Under EU regulations a validation will also be required for such a pilot to fly an aircraft registered outside the EU if the operator of the aircraft is based in the EU. For example, if the operator of an N-registered aircraft is based in the UK, the holder of an FAA licence will have to hold a validation issued under EU regulations by the CAA to fly the N-registered aircraft in Europe. (Again, this is deferred to 8th April 2014 for private flying).
Under European regulations an individual licence holder may only be granted a validation once. Repeat validations are not permitted. A validation is issued for one year. If the pilot is training to gain an EASA Part-FCL licence the validation may be extended once by the State that issued it to allow a reasonable time to obtain the Part-FCL licence.
Taken from the CAA Website. Going by that the Private Holders are safe for now!