As Beerhunter and Steve already wrote, a sporterized Enfield No. 4 Mk1.

Made by the Royal Ordnance Factory Fazakerley (that's the "F") and "FTR"-ed by the same factory.

Fazakerley was assigned number 20000-29999 with single letters and double letters from HA up to PF (these were Mk2s).
The very last No.4 series (Mk2) was the UF55A series.

So PA 299951 is one of the very last of the PA series, and a fairly late Mk1.

Patrick