Anyone heard of Marlboro bikes?

Youll probably find that the above bike uses 26 1 3/8" rims & tyres.

In which case you are in luck as that is the size they use in cycle speedway. Archie wilkinson (who have a wheel factory & sell affordable but top speedway parts) sell a range of those size wheels from £50-£70 a pair, fancy colours, sealed hubs, stainless spokes etc..

Normal town bike tyres are dirt cheap in the right places, high st shops tried to sell me a michelin world tour for £15! but they available on chain reaction for £5.99 posted!

Thats exactly the size it uses (well at the back anyway):

Technical bit:
Current rear wheel: 26 x 1 3/8 (E.A.3) 590 mm
Current front wheel: 26 x 1 1/4 597 mm
Classic MTB wheel: 26 x 1.00 through 2.3 559 mm

As mentioned though the frame is a bit too tight for that size wheel (at the back). Ideally I need something slightly smaller in diameter and thinner in width. I think I'd be best off with some 26 x 1 (650 C) wheels which are 571 mm. They're made for much thinner tyres but I could probably put some 28's on which would be thin enough for the frame without being too thin. I'm not sure how well the brakes would reach though.

thanks for the info anyway though.