If the ps3 ever came close to the 360's price in the UK, I could see it happening. That won't be the case anytime soon.
The UK is a weird spot for the ps3. It's a part of Europe, so it shares a similar pricepoint as the rest of Europe, yet the console's demand in the UK is more similar to that of the US than the rest of Europe.
In mainland Europe, the ps3 can get away with being a decent bit more expensive than the 360. In the UK it needs to at least have price parity with the Elite SKU to be competitive.
I will say that, going by percentages, the 249 pound ps3 has generally held its own against the 199 pound 360 Elite better than the $399 ps3 did against the $299 Pro/Elite in NA. Until the 360S released, of course. However, 199 vs 249 is only a 25% increase in price, while 299 vs 399 is a 33% increase, so I guess that's somewhat expected.