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The offender entered Londis, in Tinker's Drove, between 3.10pm and 4pm on Sunday 16th January.
He threatened a member of staff with a weapon and demanded cash.
The 56-year-old victim tried to tackle the offender before chasing him out of the store.
Detective Constable Tony Harlow, investigating, said: "I would like to speak to anyone who recognises the man pictured on CCTV as we believe he may have vital information to assist our investigation."
"He is wearing quite a distinctive zip-up top and I would appeal to anyone who recognises it to call police."
Anyone with any information should call DC Harlow on 0345 456 456 4 or Crimestoppers, anonymously, on 0800 555111.