IMO the best multishot is the Smith & Wesson 586. The 8" barrel is the most accurate but also the hardest to hold steady due to all the forward weight. The 6" barrel is very close in accuracy and an easier hold. I wouldn't bother with 4". Build quality is excellent with a high level of realism. It also has the best trigger out of all the Umarex range IMHO.
Someone mentioned Tokyo Marui (TM), these are airsoft pistols and come with strict caveats concerning ownership. They are VERY realistic and great fun. I like them especially because they are non lethal, well maybe not to caterpiller, but you get my drift.
Check these links for more info.
http://www.eliteshootingcentre.co.uk/
http://www.justpistols.co.uk/index.html
HTH
UBC Resident Cowboy
St Paul of 55
Been there, bought it, tried it, sold it