A suggestion rather than a recommendation (I bought the 8964U model for the first aid room at work).
WeightWatchers 8962U. I don't know if they are Class 3, but they do have a 10 year guarantee.
Looked at a few websites. These seem to be the cheapest
Why don't these websites be upfront about their post/packing charges? On some websites you have give your name/address before getting to the part of the checkout that tells you the p/p charges.
The 8964U has 4 load cells so *should* be more repeatable.
Ebay £21 inc postage for a "graded" one