Facebook’s final tax bill in the UK is likely to be reduced by more than £20m as a result of years of reporting losses in Britain, despite its pledges to pay more to the Exchequer.

It emerged on Friday that the social media company plans to alter its controversial tax structure to register more of its advertising sales in the UK, following pressure on multinationals to contribute more to the public purse.

But, while Facebook’s UK advertising revenues are worth hundreds of millions of pounds, the company said that under the changes only a proportion of that – sales to major buyers such as Tesco and WPP – would be recorded in Britain.