Walmart's lead by reducing the Titanfall Xbox One bundle to $450. Target, Microsoft and Amazon (with the promo code XIAMAZON) are all offering the Titanfall bundle with the $50 discount, and both Target and Microsoft have the same price on the Standard bundle that includes a Forza 5 code.
The Microsoft Store denotes the bundles as "limited time discounts," so don't expect the reduced price to hang around for long, even if the console got a permanent price drop in the UK. On a side note, our pals at Engadget spotted Amazon getting a bit overexcited this morning after the retailer briefly marked down the Forza Xbox One bundle to $400 with the XIAMAZON code applied. It looks like it was an accident, though, since the bundle is back up to $499 and the code no longer works with it.