Common answers tend to be either Bosch or Miele (although, you may struggle to get Miele on a £500 budget).
I've had AEG, Kenwood (a badged Fisher&Paykel machine) and Hotpoint.
Believe it or not, I have had a good experience with the Hotpoint machines, they wash and dry really well; cannot attest to the longevity, as had not had it that long and unfortunately, Hotpoint are not what they once where.
My parents have a Hotpoint DW and again, great wash and dry results and it must be at least 6 years old.
Unless going for a Miele, I personally don't expect any more than 3-5 years from ANY machine anymore (and that is probably being generous). It is a race to the bottom now to make them as cheap as possible, and of course, appliance makers/retailers are happy for us to constantly replace.
It really makes me chuckle when I read reviews of a £200 appliance and someone comments "I hope I get another 10 years like my last machine". Hahaha, never going to happen.
Coincidentally, I was taking my Vax Air vacuum apart today, to wash the brush bar and bleach down the suction head. It's a new machine (bought November 2015) and Vax have made it so that it is near impossible to service, it does not come apart easily. They want us to buy, buy, buy.
Sorry for the rant.