Owners of Senior's on Clifton Street received a phone call late on Friday – just hours before their new shop's official opening – warning them the building would be burnt down.

Following the call at 10.30pm workers living above the shop were evacuated and a police surveillance van was parked outside.

Officers also made regular patrols outside the shop.

Alistair Horabin, co-manager of the family-run firm, said: "Of course we were worried when we received a call like that – at 10.30 the night before we opened.

"But having said that, everything has still gone ahead as normal."

Police confirmed the threat to petrol bomb the Clifton Street shop and that officers had stepped up patrols in the area.

Detectives were today attempting to trace the source of the threats.

A Lancashire Police spokeswoman said: "We received a report of threats to burn down the new Seniors chip shop in Lytham before its official opening on Saturday.

"Police advised employees in a flat above the shop should evacuate the premises as a precautionary measure.

"A CCTV van has been parked outside and patrols have been passing regularly on foot. Detectives are making further inquiries."

The family-run Senior's firm has been extending in the last four years.

Having established restaurants in Normoss and Thornton, and after winning awards and growing in popularity, they opened outlets in Knott End and now Lytham.

Mr Horabin added: "We are doing our best to provide a top quality service to the Fylde coast, and we want to do this in Lytham too.

"We opened on Saturday, and had a constant stream of customers al day.

"We want to work with everyone in Lytham, and bring a positive contribution to the area.

"The weekend has shown how popular the chain is, bringing more shoppers to the town."