The legal definition of ceiling is cloued cover of broken or overcast (5 to 8 Okta).
Consequently, if flying above a cloud cover of broken then one is flying above the ceiling. While one may be able to see glimpses of the surface, it can not be relied upon. That is why I would recomend that in the case described, don't plan to fly over anything more than scattered.
A word of caution though - have a good read of the criteria for the met office reporting cloud cover. They report the lowest cloud and then before they report the next higher band, it must amount to 4 Okta (can't remember the exact figure). However, it could be 4 okta.............So with the only reported cloud being sct020 (say 2 Okta), there could be a cloud layer (or layers) just above that of 3 Okta which is not reported............get above that lot and you could end up with 2+3 = 5/8 ground cover from your height and perhaps even more if there is another few okta between you and the second layer.
Remember also that METAR and TAF refer to the vicinity of an aerofrome only. Check enroute weather also.
VFR on top is only permitted by UK pilots who have had further training in the form of an IMC rating and by every other JAA PPL without further training. Want VFR on top - move your PPL to France or Ireland or another JAA country.
Regards,
DFC