This might just be Tesco having a spring sale or it could be them getting ahead of a formal announcement from Sony UK. Either way expect cheaper PSPs elsewhere soon as others follow suit. Which can only be good news, what with most PSP games being pretty cheap either new or second hand, or even on the PSN store.
Having had a look around, Sainsbury's is only selling the PSPGo at £225, Game has PSP-3000s in for £130 with HMV doing them for £142. If you know of anywhere with them (new) as cheap or cheaper, let us know.