It's one of British cinema's imponderables why Tara Fitzgerald seems to get her kit off in practically every film she's in.

Is the disrobing a dramatic comment on the constraints of costume on a bohemian free spirit. Or is she just hot?

Here it's just a little over ten minutes before the boys are out of the barracks and Tara's euphoric about the feeling of rain on bare skin.

At least this time she offers up some sort of explanation for her frequent states of undress - "it was an experiment in flesh tones."

Fitzgerald is former artist's model Topaz, a name which gives you due warning about what sort of characters we're about to meet.

She is the second wife of barking mad Mortmain (Nighy), who's been suffering writer's block since his first and only novel was published years ago.

They're holed up in a crumbling Suffolk castle with Mortmain's son and two daughters from his first marriage.

There's Rose (Byrne), the beauty of the family, and Thomas (Joe Sowerbutts), a Harry Potter type but without the magic.

Then there's 17-year-old Cassandra (Garai), whose diary of the lifes and loves of this eccentric bunch forms the narrative.

Changes comes with the arrival of American brothers Simon and Neil Cotton, whose relationship with the two sisters provides the romantic drama.

This is a bit Little Castle on the Prairie relocated to an English countryside traversed by pristine vintage cars, midnight swims in moats and wearing upper class affectations.

The romances between the sets of siblings never catch fire although Rose does a passable Twit Girl impression (but not as good as Victoria Hervey).

The flowery dialogue, while throwing up the odd waspish gag, remains firmly earthbound and ill serves Dodie Smith's novel on which it is based.

Indeed, most of the humour isn't intentional with Mortmain coming up with a cracking observation about his dying first wife.

"I knew she was ill - even when I went for her with the cake knife."

Capture it on video.

Tim Evans