If you think about it, to get to the position where you are VFR on top you either
a. climb through cloud and find it's sunny up there (by luck, reading the forecast or asking for pireps)
b. climb through a hole in cloud but know that the cloud becomes more solid as you go along your route (but will be VFR at destination).
a. of course you could only do in the UK (assuming you only have an IMCR); b. is what you would do if you were abroad at the time.
Tim