At around 2.30pm this afternoon a woman entered Yorkshire Bank on the High Street and demanded money from staff by claiming she had a gun, although no weapon was seen.
The woman made off with a quantity of cash and was seen turning right out of the premises onto the High Street, towards Vine Street and the Angel & Royal Hotel.
She is described as wearing a black vest top, black trousers, and had a black coat over her head.
She had dark hair, was of medium to large build, and was thought to have been aged around 30 or 40.
Anyone who may have seen a woman matching that description, or who may have seen or heard anything suspicious around the area of the bank at the time, is asked to contact Lincolnshire Police on 101 quoting incident 250 of April 30.
Alternatively contact the independent charity Crimestoppers anonymously on 0800 555 111.