I to attended a very reputable school in the principality of bournemouth and i too went over by several hours as did pretty much everyone , thisis bound to happen unless you nail every learning point on the head every lesson without a hitch .
You also have to factor in possible test failure as the retest fee is just as silly as the initial plus hire of a/c , you can be the ace of the base but it only takes a wee brain fart on the day and youve partiallled there goes another 6-800 quid .
You dont need to factor two tests for the meir if you do the cpl in a twin as the cpl and mep test can be carried out together but this again is anotner cost issue .
At the end of your ppl you will have a minimum 10 hrs p1 not 20 unless you go significantly over , but this is likely to be dual time not p1