You may have seen on Jim's Wargames Workbench that book remainder store The Works* were selling a "British Armoured Tank" kit that made a reasonable approximation of a Challenger II, albeit sporting some kind of railgun instead of a cannon... Whatever, it looked useful for 28mm scale moderns with a bit of work, or near future SF with a bit of imagination.
Intrigued I popped into the Bristol store this morning and after some rummaging around found not only the "British Armoured Tank" but also "American Armoured Tank" (and Attack Helicopter - an Apache, Special Force Helicopter a Black Hawk and Stealth Plane an F117). As they cost just £2.99 I bought one of each.
To call them basic is a bit of an understatement but they are reasonable approximations of the M1A1 and Challenger II, even if the latter will need a new gun and the former some filling under the gun mantel.
I'm considering painting them up form my stalled modern English Civil War project, adding some stowage, camo netting etc to disguise any obvious shortcomings.
* Edit: I've just noticed that Jim picked his model up at The Entertainer. I'm not sure why I read that as The Works yesterday going there today to find them. Weird...