The Premiere 520 with a 1200 spin comes in at the bottom at about £479 from www.buyersandsellersonline.co.uk. This comes with a 2 year guarantee.
Although this is the lowest model it certainly isn't low on build quality. Andy writes about build quality versus features on his main site. With Miele I believe the same build is echoed from this model up the range. (correct me if im wrong Andy). As you go up the range more features such as faster spin, washer dryer, Navitronic controls and an LCD+ display come in the equation. My neighbour has the W520 and is extremely pleased with it. This sparked me to get my Miele washer dryer.
A W1514 with a 1400 spin comes in at £549 on the mentioned website and carries a 2 year guarantee.
I know you say you have £500 to spend but the W3240 is priced at £689 on the site. Presently this comes with a 10 year guarantee so that works out at £68.90 per year or 18.9p per day for 10 years with parts and labour guaranteed. I think the reckoned life of these machines is 20 years so you can see the money here.
Hope this helps.