The PF serial numbers are used by Fazakerley in the early 50's, on their No4 rifles, if it is a 'Faz' rifle then I think you may have picked up a 'fantasy piece' as the production of No5s' ceased (1947) long before the PF prefix serial number were introduced.
Please post some pictures, the barrel (showing the 'fluting' just in front of the Knox form), and both sides of the action between the breech and the rear sights.
If it is a No5 then there should be weight reducing 'cut-outs' in the action when compared to a No4.
If it does turn out to be a 'modified' No4 and you were sold it as a No5 then you should be entitled you a refund if you bought it from an RFD. If you bought it privately then unfortunately it is a case of Caveat emptor.
The Fazakerley No5 serial numbers never made it past "AC" prefix.
Post some pics - you never know it may be the 'long lost, last No5 ever built.
Never say never with Lee Enfield's
The Arrow in the U marking is a South African military ownership marking.