you can get release dates for films at the internet movie database - uk.imdb.com. Search for the film and click on release dates on the left. Sometimes they give the date of the London premiere. You could also try the official website.
I think it's on Wednesday, as a number of sources say that J-Lo is not going to be turning up "next Wednesday". Unfortunately none of them that I found stated where it is or gave the exact date.
I've googled it many times and tried the official website, but nothing came up. LeMarchand, I read the same Sky report that you mentioned and so want to know the exact Wednesday. Found out it's playing at the West End Odeon so have emailed them to get details.. nothing so far, but.