Striking postal workers outside the Royal Mail Mount Pleasant sorting office in London. Up to 120,000 union members will take part in the two day national walk-out, which began at 4am on Thursday.

Postal workers in Birmingham picket the city's main sorting office.

A picket outside the Manchester Mail Centre. Last minute talks to avert the walk-out ended amid a bitter war of words over the increasingly politicised dispute.

A postman delivers mail on the first day of the strike. Drivers and sorting office staff are taking industrial action today with delivery staff staging a walk-out tomorrow.

A worker sorts through mail at one of TNT Post's sorting centres on the first day of the national postal strike. TNT Post is one of the many British businesses working through the Royal Mail postal strike. The company offers an alternative service to the public but due to legislation it still relies on Royal Mail for the letterbox delivery of its letters.

A striking postal worker holds a handful of badges in support of the strike outside the Royal Mail sorting office in Chelmsford, Essex.

Union leaders have blamed Business Secretary Lord Mandelson and Royal Mail chiefs for the failure to reach a deal.

A picket in Coventry. Postal workers formed picket lines outside 37 mail centres in the UK.

Royal Mail lorries stand idle at Maidstone Sorting and Delivery Office in Kent. About 42,000 mail centre staff and drivers walked out on Thursday and 78,000 delivery and collection staff are expected to strike on Friday.

Striking workers keep warm on the picket line outside the Royal Mail's main sorting centre in Glasgow.

A Coventry picket line. The Communication Workers Union (CWU) said it would be announcing plans for further strike action.