I believe that the 48 and 48p are one and the same television, but the 48 (not 'p') does not come with the stand. The 48b I have also seen, but only on one particular site - I can't remember which. This normally stands for black, but as far as I know this set isn't sold in black.
So, basically, the 48b is more than likely a 48p, but the sales people have been a tad stupid

. With regard to the stand, I too have noticed that Dixons seems to be one of the few that aren't selling it with a stand, which is odd seeing that they're selling it at the same price as Curry's, (their sister company) and Curry's TV
does come with a stand. Long and short of it is you should check with the people you're going to be buying it off to
ensure the stand is included.
Edit : It's "Unbeatable" that is selling it as a 'b'. Mind you, they are STILL trying to sell an "open-box" 48B for £1,230.97, while the new ones are priced at £999.98. Oh dear...