Should add that is UK specific. Non RVSM aircraft are allowed to transit the airspace to get above/below the RVSM area, but are not allowed to cruise in it. Exceptions are State aircraft, aircraft operating under an Airspace Co-ordination Notice or similar, or aircraft in Danger Areas or TRAs.
As you move away from the edge of Europe, the ability to transit the airspace to get above/below is removed. So you won't be able to do it in Germany or Switzerland for example.