A member of the public spoke to door staff at the Wheelhouse, Bowness, alerting them to the incident before they got into a taxi.
A Cumbria Police spokesman said: “Specialist detectives are following multiple lines of enquiry and officers will be carrying out an investigation at the scene and surrounding areas today.
“Police would like to speak to a man and a woman who may be able to help with enquiries. They were in the area of Booths around this time and approached members of the Booths staff on site to ask for directions for food outlets.
“Officers are appealing for any other witnesses, or any person who has seen anything they consider to be suspicious in or around that area.”
Booths is open for businesses as usual today.
Police are appealing for this member of the public or anyone with information to contact DS 2010 Andy Lamb on 101, quoting log number 28 of the 18th May, or call Crimestoppers, anonymously on 0800 555 111.