Definitely post your question on http://www.londonfgss.com (the London fixed gear forum - while its centred on t'Capital, theres plenty of interlopers from all over the UK on it).

Best place I've found to buy spokes (outside of a good local bike shop - which are rare in the UK) is St Johns Cycles.

As for cheap hubs:

I'd recommend either some Miches (about 50-60 quid a pair) - only downside to Miche's is that you need an ISO lockring (comes with the hubs) - same threading as Campy stuff.
http://www.ribblecycles.co.uk/detail...e=MCHEHUBT0200

IRO/Novatech/Joytech/Formula route (generic group of hubs rebadged as St Johns/On-ones/Zenith/Ambrosio (cheap decent sealed hubs) etc.
http://www.on-one.co.uk/index.php?mo...sition=107:107
http://www.cyclebasket.com/products....s_-_Track_Rear (21 quid for a rear)
http://www.sjscycles.co.uk/product-S...hole-11137.htm
etc

Or maybe consider a better quality hub like a Goldtec (60 quid)/Dia Compe Gran Compe (45 quid) in the back and a generic road hub up front:
http://www.brixtoncycles.co.uk/singlespeed_stuff.html

Or a really nice Suzue (NJS) fixed/fixed hub (50 quid) (but they're loose ball so you'll have to be a bit savy with them):
http://www.on-one.co.uk/index.php?mo...sition=191:191

Theres actually a surprising number of options now available in the UK. As always, I personally think its worth investing a little money in the rear hub as its doing much more work.

Good luck