BEST GFX CARD FOR £250ish

This chart may help you decide.
Out of the cards you have listed, in terms of overall framerates over a wide variety of games and applications, the 4870x2 is the best card, followed by the GTX 285 and then finally the 4890.
All of these cards will give you very good performance no matter what tasks you will be using them for.

Can you give us more details on your specs? The PSU and screen size are particularly importaint.
If you look around all but the GTX295 is within your budget.

Realistically, unless you get a larger monitor (16x10 at least) a high end card is simply going to b producing frames you will never see.
If you are going for a larger monitor, then look at the HD4870X2 as top of the tree with the GTX275 as next choice, it is only fractionally slower than the GTX285 and a fair bit less expensive. If you have a Crossfire motherboard the HD4770 in CF is the cheapest configuration and a stunning performer, only a little short of the GTX285 and equal to the GTX275.
With the 1280x960 display go for either a GTX260 or 1Gb HD4870, you should find both for under 160 pounds.

No, no problems at all.
I was just trying to save you a little money.
The HD4870X2 is far, far, far more than your current screen resoloution requires or will ever require. Even the HD4870 and GTX260 are really a bit too much but they are much less expensive and should last for a long while, most likely the life of the machine as long as you do not buy a larger display.
Of course, if you intend to get a larger monitor then a high end card like the HD4870X2 would be the sensible choice.