Police have named two brothers they want to speak to in connection with a series of armed robberies.
David Whittle, 27, and his brother Simon Anthony Whittle, 30, are originally from the Manchester area, police said.
The robberies, where staff have been threatened with knives and screwdrivers, have taken place at eight stores in Brighton and Hove over the past nine days.
In the latest incident, two men, one of them carrying a wheelbrace, entered Threshers in Longridge Avenue, Saltdean, just after 2000 BST on Thursday.
When the 42-year-old shop assistant refused to hand over money straight away, he was headbutted in the face by one of the men.
Knocked unconscious
He was knocked unconscious and required hospital treatment for an inch-long cut to his nose and bruising.
Detective Inspector Peter Laverick said: "After last night we know these men are prepared to use violence against anyone who may try to stop them.
"If you know where these two men are, call the police on 999 immediately."
Police linked the incident to an attempted raid just before 2100 BST on Thursday at Unwins in Sutton Park Road, Seaford.
Distinctive scar
The manager said he was threatened by a man with a tool resembling a wheelbrace but managed to push him out of the door.
The men are thought to have struck first on 30 April when they raided Threshers in Holland Road, Hove, one carrying a screwdriver, just before 1830 BST.
One of the men involved in the first attack was seen to have a scar on the left side of his neck, police said.
On May 1 at 2200 BST, two men threatened staff with a screwdriver at Threshers in Queens Park Road, before stealing cash and cigarettes.
Armed with knives
In a third attack at the Asda in Brighton Marina, in the early hours of Saturday, one man approached a cashier with a knife and took what police said was "a substantial amount" of money.
Two men, each armed with a large knife, stole cash from the BP service station in Kingsway, Hove, on Sunday at 2300 BST.
The fifth attack was on Tuesday, just after 1630 BST, when two men, one armed with a knife, demanded money at Threshers, in Western Road, Hove.
The sixth incident was at the Co-op in Rottingdean High Street just after 2130 BST on Wednesday when two men, one armed with a kitchen knife, threatened staff before taking cash and cigarettes.
Police have appealed for witnesses and information relating to all the robberies.
The robbers are described as white, in their late teens or early 20s, with a slim build and possibly northern accents.