Best low light sensitivity camera under £1000
Can't say about the best, but I do a lot of low light photography using a Canon 5D and it gives me good results. I need some depth of field also, and with a zoom lens shoot at ISO 1600 at about 5.6, 100 to 300 mm, with image stabilization or a tripod. I've used 3200 as well, on the 5D it is not really 3200 but actually one stop underexposed, so I use 1600 and boost the images in post processing using Aperture. There is very little image noise, considering, but sometimes I will use Noise Ninja if it is called for.
If the 5D is too much money, look at the 40D which is easily in your price range. Not quite as good at 1600 but not bad either. I have used it as well, because sometimes (in a concert hall) I need a really quiet operation, and get it with the 40D using Live View.
I am hoping my next camera will allow me a quiet operation and ISO 3200 or 6400 without post processing. I am told the Nikon 700D does that, but I am not ready to switch at this moment. That is out of your price range anyway.