Nikon FM, great reliable workhorse camera! Lots of used ones with plenty of life left in them.
Yeah, the Nikon FM is a very solid camera that I always find useful to have aroundit doesn't require any batteries to runand it's just a lot of fun. You should be able to pick one up for under £50 on eBay or if you can find one for sale on here.
I'm also a fan of the Nikon F-801, which I think is a very underrated camera. Its viewfinder is huge with good eye relief, it autofocuses with AF-D lenses, the focusing screen shows depth of field down to at least f/1.4, and it runs on readily available AA batteries. And oh, I bought mine for exactly £5.20 off of eBay!
Be forewarned, however, that neither of the above will work very well with G lenses (both of these cameras require an aperture ring on the lens) and the Nikon F-801 won't autofocus with AF-S lenses (well, neither will the FM either, but that's to be expected).
If you need something that can work with AF-S and VR lenses, I used to have a Nikon F80 and I always thought it was a good little camera. The viewfinder is smaller than the other cameras I've mentioned, but it's probably better than any other digital cameras. I believe that the early Nikon digital cameras like the D50 are also based off of the form factor of the F80, so it should be easy to get to grips with. I've seen plenty of these available for between £20-£30 or so on eBay.
What Nikon lenses do you currently have? Keep in mind that crop sensor lenses which are designed for APS-C Nikons like your D50 will suffer from severe vignetting, although they will still mount.