The talks come as new research reveals how much strike action is costing the country's economy.

London Chamber of Commerce estimates the row has cost the capital’s economy alone £500 million since the start of summer – with £200 million lost during last weeks two day walkout.

Over the weekend staff returned to work to try and clear the backlog of letters.

Royal Mails bosses estimated 30 million letters were left undelivered, but other sources believed that figure to be considerably higher.