I would say it was both bigger
and smaller. Bigger because, it's a smaller country so people and places of interest are quicker to get to.
Plus, there's all sorts of cool 19th century history and such. Not to mention that the UK has been a melting pot for a whole mess of alternative and street culture of all sorts. Not to mention the music!
However, as opposed to America, there's a much smaller population and steampunk is still quite an underground thing, so it might be a bit smaller than the US in terms of numbers. But really I have no idea about this. :p
As you can see, there's quite alot of steampunk stuff going on and as I've already mentioned, the size of the country means you can get pretty much anywhere within half a days travel.
However, the UK is a strange land, it's not all bowler hats and cups of tea! If you were thinking about emigrating, why not try having an extended holiday here? Or do some volunteering to get a taste for UK life and culture?
In fact, if you do wish to move to Britain you'll have to pass the
Life In The UK test!
xd