Looking at spending £700 max on this and have found the following options:

1) Used Roland HP101 - £500
2) New Yamaha YDP140 - £590
3) New Casio AP500 - £650
4) New Casio AP220 - £700

Which of these should I go for, or what else should I be considering?

i am not sure about other brands, but i did spend much time researching the yamaha.
And, people always recommend YDP160 instead of 140. A bit more expensive but much better sound and key feeling. hope it helps

Thanks, but looks like that one is nearly £1k which is just too much for now.

blue78, could you supply the links to the manufacturers' model web pages?

Edit: The AP-220 seems to have the better keys compared to AP-500.

Which is understandable since the AP-220 model is the newer (current) model. Casio upgraded the keyboard action and layer sampling across all models. The AP-500 is the older model, but it was the top-of-the line model in the Celviano line in its generation (if I remember right) so it's bound to have a lot of extra features. The AP-220, on the other hand is the most basic Celviano model in the current lineup.

Ok, so which one offers the best value and which one will be best to play?

Is the new AP220 worth paying £200 more for than the Roland?

Please give a link to the Roland, for us to make a guess at.

I'm still just guessing but the AP220 Acoustic and Intelligent Filtering, seems to be more advanced than the Roland sound system. £200 is not much money in the long run.