Cheapest pre-order out there I'd say at £36.97, plus £2.15 in points to spend on your next purchase at Rakuten, and up to 6.3% cashback via TCB.

*** Use code MAYDAY to take 15% off until May 29th. ***

***** UPDATE *****
Looks like Base or Rakuten raised the price then pulled the listing for the pre-order. Don't worry though, you can still pre-order from Boss via Rakuten:

http://www.rakuten.co.uk/shop/bossdeals/product/50879/?l-id=gb_search_grid_product_1

A few pennies more but still a great deal.

***** UPDATE 2 *****
Now available from Simply Games (still via Rakuten) for £37.27 after code:

http://www.rakuten.co.uk/shop/simplygames/product/20290/?l-id=gb_search_grid_product_thumbnail_2

...and The Game Collection for £37.36 after code:

http://www.rakuten.co.uk/shop/thegamecollection/product/14663/?l-id=gb_search_grid_product_thumbnail_6

Shopto have it for an extra quid or so (£38.12 after code), probably a safer bet if you're concerned about getting it on launch day:

http://www.rakuten.co.uk/shop/shopto/product/PS4UN00/?l-id=gb_search_grid_product_thumbnail_4

Official blurb:

Set three years after Uncharted 3: Drake's Deception, Nathan Drake has presumably left the world of fortune hunting behind. It doesn't take long for adventure to come calling when Drake's brother, Sam, resurfaces seeking his help and offering an adventure Drake can't resist. On the hunt for Captain Henry Avery's long-lost treasure, Sam and Drake set off to find Libertalia, the pirate utopia deep in Madagascar. Uncharted 4: A Thief's End takes players on a journey through jungle isles, urban cities and snow-capped peaks on the search for Avery's fortune.

KEY FEATURES:

- Next-Gen Blockbuster Adventure: Uncharted 4 ushers in a more cinematic experience on the PS4 system with real-time cut scenes and new character animations to highlight Naughty Dog's signature storytelling.

- Dynamic Gameplay: Evolved mechanics give players many fresh approaches to gameplay, including new rope and grappling mechanics, added climbing moves and equipment, and seamless fluidity between melee, stealth, and combat.

- Expansive Environments: Varied and richly detailed environments open up with multiple navigation paths to encourage exploration. Gameplay and enemy AI strategically leverage the wider design and added verticality.

- Drivable Vehicles: For the first time in Uncharted history, drive vehicles during gameplay to make big moments even more spectacular and interactive.

- Uncharted Multiplayer: Uncharted 4 will continue to evolve the franchise's multiplayer experience on PS4.