Mr Cameron visited McKanna Meats in Bloomsbury, central London, and hand delivered a letter which urges the company to check whether it is entitled to the £2,000 National Insurance break.
He spent about five minutes chatting to a partner in the butcher's, Graham Morley, and also bought some sausages. Speaking afterwards, Mr Morley said he was not sure how much difference the tax break would mean to his business.
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The operation to recover the unexploded bomb near the Houses of Parliament let to disruption in central London overnight.
Southern parts of England and Wales will see sunny skies after a frosty start.
A police spokesman said the incident in the Bourke Street Mall on Friday was not related to terrorism.