The growth in online sales of goods was ‘significantly’ slowed by the wave of strikes by postal workers, leading to a £53m fall in sales, according to a new study today.

Sales have improved all year, but were reported to have plunged by 5% in the last week of October, when members of the Communication Workers Union were taking action in a long-running row over pay, jobs and modernisation.

The IMRG Capgemini e-Retail Sales Index showed British shoppers spent £4.2bn online in October, an increase of almost 12% on the same month last year.

Mike Petevinos of Capgemini said: “E-retailers must heed the warning signs and act to reassure consumers that orders will be delivered in time for Christmas.

“With consumer confidence restored, e-retailers can get on with the real challenge of convincing consumers to spend online.”

Tina Spooner of consultants IMRG, the e-retail industry body, added: “Whilst the index returned to double-digit growth in October, the decline in e-retail sales during the second half of the month shows that consumer confidence was affected by the Royal Mail strikes.

“With the threat of further strike action averted, shoppers' concerns around delivery will no doubt be dissipated.”