Because I Said So (12A) <!-- none onestar twostar threestar fourstar fivestar -->

Only a sadist would insist on taking a date to the crummy Valentine comedy Because I Said So. Warning bells will ring for anyone acquainted with Diane Keaton's recent comic output - Hanging Up, Something's Gotta Give and The Family Stone are movies I dearly hope I never have to see again. If you think that lot's bad, though, how about this trio, from the pen of the co-writer, Jessie Nelson - Stepmom, The Story of Us, I Am Sam. Apologies to those whose memory I might have jogged with that list.

Keaton plays Daphne, a divorced mum who has raised three daughters on her own and seen two of them happily hitched. Now she wants to marry off her youngest, Milly (Mandy Moore), and secretly goes online looking for Mr Right. Soon enough Mom has set up her unsuspecting daughter with a smoothie architect (Tom Everett Scott), but she'll have to see off the hunky blues guitarist (Gabriel Macht) that Milly has just hooked up with.

Even if this were a plausible comic premise, Keaton's character sets one's teeth on edge. She's clearly meant to be dizzy and adorable, but is, in fact, simply a controlling busybody who puts the "mother" into "smother".

Nelson evidently has no sense of humour, otherwise she wouldn't run the terrifically unamusing scene (twice) in which Keaton's dog watches internet porn, or have her share inappropriate sexual revelations with her daughter. The film's destination, ending a purgatorial journey through "life lessons" and "personal growth", can be glimpsed a country mile away. It's all as cosy and interesting as an old bed-sock.

At one point Daphne warns Milly, "You're going to end up like some pathetic character in a Tennessee Williams play." If ever a film could have used a character from a Tennessee Williams play, it's this one.