Chatting to Richard Hudson a few weeks ago, he said H and H's tie sales had gone up a lot in the last year or so and that he saw an increasing tendency (I paraphrase) for those with the option of biz caz or suit to dress more formally than a few years ago.
That's also my impression: even if - sigh - it's just men upgrading biz caz to a suit with no tie.
I suspect it's psychological. A bit of serious times require serious clothes, a bit of contracts and clients being harder to get so why risk giving a casual impression, and a bit of mental armour. If for the first time in your adult life you are genuinely worried about losing your job or paying the school fees, wearing some form of proper business dress may make you feel more secure. "You can't sack me, I belong here."
I also think I detect a parallel ratcheting-down of the ever-popular English loud -checked/bold-striped shirt thing too. A more humble era for Western capitalism is causing a reaction against items seen as swaggering, arrogant., BSD, "Wall Street" (the movie) and so on. Mad Men probably has an influence too.
I wear a DB fairly often and am overdue a new one. I very rarely see others in central London. I think that's in part simply because all the DBs that were so popular in the 80s and early 90s (the boxy flappy low gorge often 1 show 2 things) have either been abandoned by their owners as outmoded or, more likely, have simply worn out and everything in the department store that our typical bloke reluctantly buys his work clothes from is an SB.