How close are you to central London? With that budget you won't be able to buy the same type of ring that, say, Victoria Beckham might wear but, equally, you ought to be looking above the type of stuff that H Samuel mainly offers (most of which, to my uneducated eye, appears to be grossly over-priced for what you get). You ought to be looking to see what you can find in the independent retailers in Hatton Garden:
http://www.hatton-garden.net/ring.html
Alternatively, if you're closer to the Midlands, you'll probably find something suitable in one of the many independent shops in Birmingham's Jewellery Quarter:
http://www.the-quarter.com/index2.htm
(Click 'Jewellery Retailers' at the top left).
As I assume that you're looking for a new eternity ring (because I answered your previous question on the subject), it would seem a great idea if you and 'Mr Poison' (to use your name for him) could make buying it a special day. So why not have a lovely day out in London or Birmingham (perhaps with a meal in a posh restaurant or taking in a show) and go home with a beautiful memento of the day?
Chris