Three interesting posts from Shoestring Flyer.
Post 45: QFE may be good for you when landing and in the vicinity of the aerodrome (circuit), however once you move away from those environs do bear in mind that the base of controlled airspace, where defined as an altitude, is based on the relevant QNH. Head away from your airfield on QFE and (in pretty much all of the UK) you will already be x feet above sea level. This may cause you difficulty, because you are now flying at a height, which may put you close to or even above the base of CAS (altitude) of which you may not be conscious, because you are flying on QFE. Or do you do the relevant mental arithmetic whilst flying to prevent an inadvertent infringement.
Post 49: At peril of engaging in a north-south, hills-flatlands and QFE-QNH debate, to which others have alluded, I find it remarkable that pretty well all commercial operators, including single pilot operators, use QNH and manage the mental arithmetic involved. I would suggest that adding the elevation of your landing strip to the relevant QNH and then flying it accurately should be well within the competence of any qualified pilot; it is, after all, simple mental arithmetic.
Post 55: Regarding the RAF; sadly, it is a somewhat minor player in aviation these days and it's historic adherence to QFE is not reflected by the major players - the airlines, whose use of QNH is pretty much total. To that end all professional flight training operators will use QNH as part of the process of preparing their students for commercial operations.
It is also worth considering that all UK civil ATC units will use QNH as the basis for providing the vertical separation of aircraft under their control, and are unlikely to make adjustments for the personal preferences of pilots who don't give a stuff what ATC say. Even if you request and are given a QFE, in addition to the airfield QNH, you will be expected to state your vertical position by reference to the QNH, as an altitude.
Fly safely, and do bear in mind that the charts mark elevation related to sea level.