Firstly, you do not have to convert to fly in the UK – until 08th April 2017.
Some reasons for wanting an EASA PPL might be to get a UK rating such as an IMC rating, or you might not be able to renew your foreign licence here and are unable to go back to your licence country every one or two years to revalidate/renew it.
There is a good reason soon, with EASA being introduced in the UK you will require a validation or EASA licence after 08th April 2017, so you may wish to convert to a EASA PPL. Details of conversion requirements are contained in CAP 804, Section 4, Part Q.
In the case of private pilot licences without an instrument rating, the holder shall comply with the following requirements:
(a) complete the PPL written examinations for Air Law and Human Performance;
(b) pass the PPL skill test as set out in Part-FCL;
(c) fulfil the relevant requirements of Part-FCL for the issue of a type or class rating as relevant to the privileges of the licence held;
(d) hold at least a EASA Class 2 medical certificate;
(e) demonstrate that you have acquired language proficiency in accordance with FCL.055;
(f) have a minimum experience of at least 100 hours as pilot in the relevant category of aircraft.
Please contact me if you need to complete these examinations – I can conduct the ground exams and/or Skills Test and/or Radio tests. If you have less than 100 hours PIC, then please contact me for advice – it is still possible to convert, but the requirements are assessed on an individual basis and are submitted to the CAA by the Approved Training Organisation.