A Lisburn man contacted the Star to explain he had purchased petrol at Tesco in Ballymena over a period of three weeks at an average cost of £86 per fill.

Tesco, he added, gave him a five pence per litre voucher back with each fuel purchase.

"Other members of my family have been filling up similarly in Tesco, Lisburn but have not been receiving the same 5p per litre voucher with their fuel purchases," he continued.

"This weekend past, I filled up in Lisburn and likewise did not receive the voucher. On this basis, it would appear that Tesco customers in Ballymena are paying five pence per litre less than Tesco customers in Lisburn. The pump price is identical. Is this fair pricing?"

However, a spokesperson for Tesco explained the discrepancy had arisen because of a mistake at the firm's Ballymena petrol station.

"Until November 30, we are offering customers who spend £50 or more either in store or online, a coupon which gives them 5 pence off every full litre of petrol or diesel they buy, up to a maximum of 100 litres," she said.

"The promotion is very popular and this is the third time we have run the scheme since the summer."

The spokesperson said the promotion's terms and conditions stated the qualifying spend 'excluded purchases from any Tesco petrol filling station'.

This, she said, was why customers spending £50 or more in the Tesco petrol station in Lisburn 'or any other Tesco petrol station' did not receive an additional fuel promotion voucher when buying petrol.

"However, I realise this was not the case in the Tesco station in Ballymena and, for a short period, customers there did receive the extra voucher when buying fuel. This was an error which was rectified as soon as it was brought to our attention."