Conduct of the CAA PPL exams is described here:
http://www.caa.co.uk/docs/33/srg_lts_StdsDoc11_v9.pdf
The relevant sections for calculators are:
2.7.9 NEVER allow the use of programmable electronic calculators (this includes those calculators that contain Flight Calculation software).
2.7.15 NEVER permit applicants to take a mobile phone or other electronic device (apart from a permitted calculator) into the examination room.
"Non-programmable" still allows quite a decent calculator. I recently took some CAA exams at Gatwick, and the "standard A-level" calculator fx-83GT did not trouble the CAA invigilator.