Hold my hands up to be totally wrong, not kept up with the changes as I should have done!
AIUI now, in the UK you do not have to abide by the VFR cruising levels, in Europe I believe You do!
The semicircular level system replaces the quadrantal system and brings the UK into line with ICAO standards applied elsewhere around the world. VFR and IFR aircraft are allocated different levels to fly at:
IFR flights use whole 1000's of feet (e.g. 1000, 3000 etc when flying eastbound, and 2000, 4000 etc. when flying westbound)
VFR flights use the intermediate 500ft levels (e.g. 3500, 5500 etc. when flying eastbound and 4500, 6500 when flying westbound)
For VFR flights, compliance with the cruising levels remains good practice but is not mandatory.