A few years ago, not that many, a 747-200F op by a U.S. company got so hacked off waiting for a slot that they filed a VFR plan from EGBB to EBOS.
I have done same route in both directions in a single and the thought of meeting a 74 opposite direction at 2,400 ft under a TMA would certainly have got the adrenalin going
Luckily, a slot came up and they accepted their IFR clearance - phew!