Adrian Harvey, 56, of La Rue du Passeur, Vale, admitted the offence when he appeared in the Magistrate’s Court.
The court was told how he had driven in to the Longstore Coop car park at about 5.40pm.
He went in to the shop where staff were concerned that he might be drink-driving and called the police.
When officers arrived, he had just got out of his van and was starting to walk away.
He provided a roadside breath sample which identified 118mcg of alcohol in 100 millilitres of his breath when the legal limit is 35.
He said he had been drinking in his vehicle after leaving the shop.
He refused to provide a breath sample that could be used for evidential purposes at the Police Station following his arrest.
He had similar convictions on his record from 2004 and 2013.
Defending, Advocate Alan Merrien said his client had been given a four-pack of beer before going to the shop.
He had drunk this in his van after leaving the shop so the 118 reading should be ignored as there had been post-driving consumption which had put the reading up.
He had put the vehicle’s keys in a lock-up box before he started to walk away.
He had not been in trouble at all since 2013.
Deputy Judge Russell Finch imposed a prison sentence of six weeks suspended for two years, with a licence suspension of three years.
He said he wished to commend the public-spirited actions of the Coop staff who had called the police.