Depends how you measure "fast" - and how you measure "production". =o)
The Ultima GTR 720 holds the record for 0-100mph-0 in a staggering 9.4 seconds.http://netshow.inetc.net/ultimasports/UltimaRecord2006.wmv
It's also taken the Top Gear record for the lap time around their track, knocking a good few seconds off the Zonda and a lot more off the Bugatti.http://netshow.inetc.net/ultimasports/TGLapRecord1.wmv
Here's a list of the records it holds.http://www.ultimasports.co.uk/Content.aspx?f=records
Their aim is to get one around the Nurburgring in 6-and-a-half minutes!
The boss, Terry Marlow, is currently working on an 820bhp version, which should be pretty special.
And one is being privately built with 2 force-fed nitrous motorcycle engines which should develop over 1000bhp as well as providing 4 wheel drive.
Is it a production car? Take 70 grand to Ultima and they'll hand build you a car with the same specification and standard as the record holder.
Probably in less time than it would take Bugatti to deliver you a Veyron.
But you also have the option to build it yourself, so it's also a kit.
Ultima recently took another record, getting around the TopGear track in 1min 9.9secs.
Apparently a certain Mr. Schumacher in a million quid's worth of Ferrari FXX only mananged 1min 10.7seconds.
The most surprising thing, though, is that the Ultima was driven home afterwards because it managed the time in a road legal setup.
Unlike the Ferrari.....