Marco, it seems that Sugden have had a few model changes in the last fifteen years or so. HiFi dave has bought in a current A21 and loves it to bits, although he claims the other models are a bit softer-toned.
The A21 I knew well, as it was a loan amp for a few years, actually sounded a bit brightly lit and slightly messy. I happily admit not to looking inside, as various bits may have needed replacing and the thing properly set up.
While we're on UK made amps of substance (and I don't mean recycled 1950's PA amps), the current Rega Elicit should be considered too..
Tear down these walls; Cut the ties that held me
Crying out at the top of my voice; Tell me now if you can hear me