The UK distributor of this film is Icon, so the inclusion of the Director's Cut is unlikely.
The only Blu-ray release of "The Butterfly Effect" in the UK, so far, has been its inclusion in a 2 disc set of the trilogy, with parts 1 & 2 sharing a BD50 and part 3 on a BD25. Theatrical cut only and no extras.
Icon is also the distributor of the film in Australia where it was released as a single Blu-ray but it still only included the Theatrical Cut. The missing extras were reinstated but some of these are apparently in 1080i. The disc is Region ABC. I would surmise that this will be the disc contained in Zavvi's Steelbook.
Due to the lack of both cuts of the movie on the Icon release, I held off obtaining the Blu-ray until the US release from Warner (New Line). This definitely contains both Theatrical and Director's Cuts, as well as the extras. It's also Region ABC. I understand that the German (Warner) and French (Metropolitan) releases are identical to the US one.
Since Warner's release postdates Icon's by two years, it may be the case that Icon will have licensed the new re-mastering of the Director's Cut from them for their forthcoming Steelbook release, which will be their first release of this title, as a single Blu-ray disc, in the UK. I hope that's the case, otherwise I'll be keeping my US disc. I guess that we'll find out one way or the other this weekend.