The UK has gone from being relatively insignificant to us debating whether or not it is the second largest market in the space of a decade.
The UK is the largest market in Europe despite not having the largest population (Germany has).
The UK's market is constantly trending upwards, you never hear of people saying that the UK's market is dead, do you? Hell, look at this growth chart - http://i2.photobucket.com/albums/y24/konangrit/UKmarketevothroughsep08.jpg
Outside this current recession, the Pound tends to be very strong against the dollar, and the consoles are often much more expensive than in US, Japan - higher profits for the firms. Same goes for the actual software.
Due to the fact that the UK speaks English, there are no translation costs for American firms to release software here, unlike Japan. Lower costs = more profits.
One would imagine that advertising in the UK is also relatively cheap in the UK. After all, there's only 60 million people living here, and there's over 300 TV channels. Again, lower costs = higher profits.
With all this in mind, although the UK currently isn't second place in terms of marketshare (but it is growing, I believe) it's still second in terms of importance to the industry.
Even in output, where the Japan trumps allover the UK, the UK's importance is rapidly growing. Criterion, Rockstar, Media Molecule, and tonnes of others all are UK based - still nothing compared to Capcom, Konami, Nintendo and Co - but far more important than it used to be.
EDIT: I also recall reading something somewhere, where it said that the UK spent more money on games per person than any other country in the world. I haven't a source, atm, but I will try and find it.
