Go digging around the SWR site, and try and get an estimate of the age - looks like an oldish one to me. It may well have a multi tap transformer...meaning it can be correctly wired internally by switching a few connections. Later, they changed things so you had to replace the transformer for European voltage.
Its a good amp, so worth some time researching, and it will be worth a lot more if it is correctly modified and safe to use in the UK.