25inch to 47 is a big jump, probably too much as it implies that you don't sit too far from the screen, based on your 25inch CRT.
So the 47 will look huge and pretty awful unless you are planning on sitting a lot further away or only planning on watching 1080P content from bluray or similar.
I might suggest that broadcast HD might not be great either, as it is only 720P or 1080i, not 1080P, and so will also require upscaling on a screen of that size.
If you watch a fair amount of SD channels I would limit the size of the set to something on the lower end of those appropriate to your viewing distance, and maybe even to a 720P screen as these seem to display SD better as they have less of a job to do (and mess up) with the upscaling.
I would look at something Panasonic from John Lewis - if you buy it mail order and then decide you have made an awful mistake with the size you should be able to return it under distance selling regs.
My mate has a 42inch Panasonic Plasma and it does have a good picture but is barely acceptable with freeview SD channels (to my eyes) as the seating is only about 10 feet away.