The promotion allows shoppers to double Nectar points to spend in store at Sainsbury’s in certain categories such as clothing, homeware and electricals.

Shoppers can swap points for vouchers, but these can only be redeemed in store at larger Sainsbury’s between 11 and 17 November, not online.

Lewis claims this excluded extremely clinically vulnerable shoppers from benefitting from the promotion as they wouldn’t be able to visit a store if they were shielding at home. He had a virtual meeting with senior Sainsbury’s management this week to discuss the issue.

As a result, Sainsbury’s have now said that anyone who has already redeemed points to use in the Nectar double-up event will be able to swap them for double points to use at any time.

Martin Lewis, MoneySavingExpert.com founder, said: “I think this is a good solution and I’m thankful to Sainsbury’s for taking my call – and listening – as I did too. It was stuck between a rock and a hard place.

“I’d suggested it allow people to redeem online as well as in store, but it explained that simply wasn’t practicable in the time available as many of the redeemable goods are only stocked in store. And equally, as Sainsbury’s is controlling the numbers in shops, the amount of people going in store to redeem their double points vouchers shouldn’t have a material impact on footfall.

“That left the problem of what to do with those who simply couldn’t go into a store, due to vulnerability, yet who had changed points into double-up vouchers. These people were being deprived of the promotion.

“Sainsbury’s was planning to allow them to get a refund and get their points back. But I suggested that it’d be best if Sainsbury’s gave them double the points back, so in effect these people – some of those most hard hit at the moment – could still benefit. It has agreed, which I think is a win-win all round.”

Who can swap points back?

Clinically extremely vulnerable shoppers who have a letter from their GP will be able to contact Sainsbury’s customer service to have doubled points reimbursed.

If you’re shielding for whatever reason but aren’t clinically extremely vulnerable and have swapped points to use in the double-up, you’ll be able to swap them back but you won’t receive double points.

If you’re extremely clinically vulnerable and have already swapped your points back, you can now contact customer services to receive double your points after the policy tweak.

In all the above scenarios, you can call Sainsbury’s on 0800 636 262.

A Sainsbury’s spokesperson said: “Double-up is a promotion aimed at loyal Sainsbury’s customers to get great value when they are already shopping with us in store for essential items. We launched the promotion pre the announcement of the English lockdown and have taken the decision to continue to offer it to customers, knowing that it helps them get great value ahead of Christmas.

“Unfortunately, most of the products included in the promotion are not available to buy online, so we are unable to offer double-up online. Where clinically extremely vulnerable customers have already redeemed points during our pre-issuance period from 28 October to 3 November, we will reimburse double their points so that they can get great value again once they are able to go back into store.

“Where clinically extremely vulnerable customers have a letter from their GP, our customer service team will support them in arranging points to be added to their account.”

What is the Nectar double-up and how does it work?

The Sainsbury’s double-up event allows shoppers to swap points for a voucher which is twice the usual value.

For example, 1,000 points = £10 instead of £5, 5,000 points = £50 instead of £25 and 10,000 points = £100 instead of £50.

Customers could order vouchers online between 28 October and 3 November with the vouchers eligible to be spent in stores between 11 and 17 November.

They can be used on the following categories: electricals, entertainment, Tu clothing, homeware, Taste the Difference wine, sparkling, champagne, sherry and port, toys, seasonal, cosmetics, fragrance and skincare.

Customers must have at least 1,000 Nectar points to take part and it can’t be used for groceries online, in locals, centrals, petrol stations, concessions, Argos or Argos at Sainsbury’s.