Posh Totty! St. Trinian's star Tamsin Egerton goes for understated glamour in midriff-baring cut-out dress as she steps out with boyfriend Josh Hartnett in New York

They are one of the most low-key couples in showbusiness.

But Tamsin Egerton couldn't help but turn heads when she stepped out with boyfriend Josh Hartnett in downtown New York on Thursday.

The stunning actress, most famous for her role as one of the Posh Totty gang in the remake of St Trinian's, looked sensational in a cut-out navy dress which left her toned stomach on show.