The union said progress had been made in the discussions on pay and conditions but not enough to avert further strike action.

It said further strikes would be announced before the end of the month.

Royal Mail said it was "extremely disappointed" that the CWU "continues to ignore the stark challenges facing the company".

The British Chambers of Commerce (BCC) said further strike action would be damaging to small businesses - and to Royal Mail.

A spokesperson said:

"An agreement needs to be reached soon or yet more customers will seek alternative solutions for their postal needs."