Below is all referenced from the CAA website Available at: https://www.caa.co.uk/General-aviation/Pilot-licences/EASA-requirements/General/Theoretical-knowledge-examinations/
Theoretical knowledge examination
As part of the requirements for any EASA licence, you will need to complete theoretical knowledge exams. Which exams you will need to take will depend on the licence and aircraft type you are applying for. The aircrew regulation specifies the subject areas you will need to cover for each licence or rating, but the number of exams may vary between different European states. It is your responsibility to take all the theoretical knowledge exams you need through one European state. However, you can take the practical skill test in another state.
When can I take the exams?
You can only take your exams once an approved training organisation (ATO) such as Full Sutton, in which has recommended that you do so and after you have completed the appropriate training course of theoretical knowledge instruction to a satisfactory standard. Exams for the LAPL and PPL are sat and administered at Full Sutton Airfield. Exams administered by the UK CAA are only available in English. A recommendation to take your exams from any ATO will be valid for 12 months. After this time, if you haven’t taken at least one exam you will need another recommendation to take them. To obtain this recommendation, further training may be required.
Validity of exam passes
Your exam passes must be valid when you apply for a licence or rating. Passes cease to be valid after a certain length of time, and this validity period varies depending on the licence or rating you are applying for. For information on how long your exam passes will remain valid, see the requirements page for the licence you want to apply for. Your theoretical knowledge examinations must be current and valid at the time you undertake your skills test and must still be valid when your application is received and processed by the UK CAA.
A mark of 75% or more is a pass and there is no penalty marking. You must complete and pass all required theoretical knowledge exams within 18 months, counted from the end of the calendar month in which you first attempted one of the required exams. If you fail an exam you will need to undertake further training at an ATO, and how much training you will have to take will be at their discretion.
The LAPL and PPL exams are administered by ATOs and a session is defined as a 10 consecutive day period. In the UK, LAPL and PPL exams can also be sat at RTFs, as well as ATOs.
Theoretical knowledge examination cross crediting
The theoretical knowledge exams for an Airline Transport Pilot Licence are the most comprehensive and therefore if you have passed these already they will be valid when applying for a LAPL, PPL or CPL. All exam cross-credits are applicable as long as your passes are valid, as set out in the Validity of exam passes section above. You do not need to have obtained a licence in order for exam cross-crediting to apply. You should have received a link through your email to move any medical certificates onto the new online portal; once you have created an account this will also allow you to apply for any theoretical exams. If you still need to apply for an online portal please follow this link: https://sso.caa.co.uk/adfsweb/Register.aspx