If you're in controlled airspace, you will be told which level to fly at
I've never been told what level to fly at, only that my requested level is "not available". In any case, in the particular block of airspace you're talking about, you'll be given a vector in any case. I've never routed round the north but I'm not sure which way you'd get given as up to 6,000' is occupied by the SID's from Heathrow, Luton, Stansted etc and the levels from FL80 up to FL150 (usually) are the stacks at LAM and BNN and the traffic inbound to them.
Recently I filed Y on the flight plan to get from Lille to Fairoaks, intending to switch from IFR to VFR over DET/BIG as the standard routes seem to copy Farnborough's SID's/STAR's which are the long way round via SFD and GWC but as I approached DVR, the controller gave me direct GWC. When I "complained" about the extra 80 track miles and the longer leg over the sea, they descended me clear of all controlled airspace and cancelled my IFR portion so even an accepted plan doesn't always go your way. (The inverse had worked outbound as I flew at 2400 feet to Biggin then cleared to join controlled airspace from there).
PS To the OP, you use the semi circular rule on airways rather than the quadrantal rule you suggest in filing of FL075. You could always file FL100 then leave it to the controller to work round your slow climb (they will also vector you to keep you inside controlled airspace during a climb if necessary).
Last edited by Fright Level; 14th Jun 2008 at 22:04.