There is nothing that resembles Ashford Castle in England, except, maybe the Queen's residence at Windsor, and I doubt if she would be persuaded to take in paying guests!

English hotels tend to be more 'country house' in style, so not as large or castle-like. The nearest castle-style hotel I can think of is Amberley Castle in Sussex - http://www.amberleycastle.co.uk/ - but it's not quite in the same league as Ashford Castle.

If you want something historic, then Cliveden House in very baronial.

Four Seasons Hampshire is very good, but it is relatively modern in many respects. Equally, Chewton Glen and Lime Wood are nowhere near as old as Ashford Castle.

Depends upon what you are looking for - history or a great countryside hotel.