Made in a statement to the House of Lords, Mandelson said, if necessary, both bodies would use alternative arrangements to transport appointment notifications, blood samples and test results.

He said: "I very much regret what is happening. Candidly, I think it is totally self-defeating for our postal services and those who work to deliver them.

"Taking industrial action will not resolve this dispute. It will only serve to drive more customers away from Royal Mail."

Mandelson's comments come as the mail operator and representatives from the Communication Workers Union (CWU) are locked in talks to help avert the first spate of national strike action, currently planned for tomorrow (22 October).

Around 42,000 mail centre staff and network drivers are set to stage a 24-hour walkout tomorrow, swiftly followed by 78,000 delivery and collection staff following suit on 23 October.

Responding to Mandelson's comments, Billy Hayes, general secretary of CWU, said: "These comments will damage the talks. While the CWU and management are working hard to reach an agreement, Lord Mandelson is misrepresenting the facts to Parliament and undermining any progress being made in the talks.

"His comments about the dispute being centred on London are ill-informed and untrue."

The business secretary's latest condemnation of the strike action comes after he branded it a "suicidal act" that "defies logic", and one that could turn customers away from the mail medium.

Adam Crozier, chief executive of Royal Mail, has strongly criticised the planned strike action, calling it an "appalling and unjustified attack on customers".

Also see: Royal Mail to hire temp workers to clear backlog