Early on in the Clubcard campaign, peak traffic had reached 120Mb/s, with Akamai's Dynamic Site Accelerator services in the cloud offloading 90 percent of this from Tesco's servers.

Last year, in another Clubcard promotion before Christmas, tills at around 100 Tesco stores following a routine IT upgrade, with some being forced to close as a result.

Those customers who missed out on doubling their Clubcard vouchers this year are being encouraged to contact Tesco customer services.

Tesco said in a statement: "We experienced a huge last-minute rush over the weekend. This meant that some customers were not able to exchange their vouchers or had problems with the process, and missed the deadline of 5 December. We are doing everything we can at our customer service centres to help those customers affected."