I'd say Spectrum, just down from Warren Street tube station is your best bet.
The will have most if not all of these lenses in stock. Just go armed with the best prices you can find as their first question is usually "How much do you want to pay?"
You can usually get a good (fair) deal but you may have to haggle a little. (They say they will match anyone elses price as long as the other place has it in stock.)
They are a bit odd in that they won't usually tell you a price straight off so do your research first.

You're not kidding. You could get a return flight to New York and pay the dollar price and still come out just under the UK price.

UK price £599.99 US price $539.99
How does that work then.

If it's as good or better than the 18-55 ALII/WR I'll be first in the queue. Ok it's not that fast ( not a problem on a K5!) but it's a good size, great range and WR. Long overdue but very promising, on paper at least.

Missed it. Was it any good?

I'm looking forward to the 20mm f2.4 next........

Glad to see you're still "popping" in to see us.

Thse are amazing. Not at all how I expected a bubble burst to look.

Well here's another vote for the 100 macro. It's wonderfully sharp and the macro facility opens up a whole new world. Plus it can be had for £300 in Currys/Dixons/PCworld at the moment.

I'm also "QUITE" happy with my k20D but I would like to see improved high ISO noise performance. Autofocus isn't always as fast or as accurate as I would like (but that's not a major concern for me really.)
Probably just me .....But, what I would like is a fast way to disable autofocus on shutter push without diving into all those menus.
Or for instance the ability to assign it to the AF button only in "user" mode. So when you hand the camera to someone else , the camera will still autofocus on the shutter push when you take it out of "user" mode.
Oh.... and about the size of an MX!
With 1080 video at 25fps

The 40 is an excellent lens. I too wanted the 35 macro ( which is also excellent and perfect for a digital walkabout lens) but I bought the 40 when I stumbled across a new one for a shade over £200. Now I can't justify getting the 35.
The 40 is so tiny that I can get my K20 in a coat pocket when that lens is attached. I focuses faster than any of my other lenses and is incredibly sharp, even wide open (and it turns Canikon owners green)

I ashamed to say it doesn't really get as much use as it deserves as it could probably cover 75% of my photographic needs if I moved about a little bit more.