According to Sussex Police, a man with a pair of red boxer shorts covering his face entered the Tesco Express store in Station Road, at 6.15am on Sunday, and demanded money.
Police said the man left with a quantity of cash and those working inside the store at the time were uninjured but very shaken.
A spokesperson said: “A 25-year-old man has been arrested on suspicion of robbery.
“He has been released on conditional bail until September 27 while enquiries continue.”
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