Hi Darren!
The top recommendations here are usually the Alaska (80x50cm) or the Barney or the Alexander (100x50cm) for barred cages. All available on zooplus.co.uk.
Tank-style cages are a little harder. You can use an IKEA display cabinet turned on it's back as a tank (involves a DIY lid) or you can look for secondhand fishtanks, like 55gallon+ or go the full hog and DIY your own (best way to get maximum area/£).
If you look through the
Let's See Your Cages thread for something you like the look of you can go from there.