It appears to come as a surprise to controllers and pilots who are used to the situation in other countries (Oz and the USA in particular) that the UK does not have a standard TA/TL, and that it tends to be a lot lower than in those other countries.
What you need to bear in mind is the size of the UK, which, together with the density of population, the density of airports and therefore density of controlled airspace and density of air traffic, requires active Air Traffic Control down to a much lower level.
Furthermore, we do not have fantastically high lumps of cumulo-granite so above 4,406' there isn't so much of a problem with inadvertently bumping into the terrain. It does happen, of course, but you need to try a bit harder than you do in some parts of the world.
In my previous airline when the SID ended at a FL, we took off on QNH and setting 1013 was one of the post-take-off actions (which triggered the request for the after take-off checks). For reasons that, I am sure, most people here can understand, I am not entirely happy with the concept of SIDs ending at a FL rather than an altitude.
I believe (I may be wrong) that PANS OPS says you can set 1013 when less than 2,000' from TL and cleared to a flight level. You may be making difficulties for yourself if you set 1013 immediately you are cleared to a FL since you may be asked for your passing altitude on the way. In some machines I've flown, climb performance was not brilliant, so getting to within 2,000' of TL could take a while!