Just freecalling for airways/LTMA entry is not likely to be allowed.
I was reffering to you flying an approach into somewhere like Biggin Hill/City/Luton etc etc (even LHR!), where from DET I could climb you up to 4000 feet in the LTMA.
Just freeecalling asking to route DET-BIG-BPK at 4000' might get a different reply...!
There is probably something in the AIP saying that you must submit a flight plan. (This is how the "Flight Progress Strips" are produced for the relevant sectors for controllers to write on)