The Communication Workers Union has voted for a national Royal Mail strike by a huge majority, threatening severe disruption to postal deliveries across Britain.

The vote by Communication Workers Union (CWU) members, who have been embroiled in a bitter row over jobs, pay and services, resulted in a 76 per cent majority in favour of a national strike, the union reported yesterday.

The CWU said its 121,000 members backed a nationwide walkout by 3-1 in protest at the “imposition” of changes to working practices as well as cuts in their pay and job losses.

The union will have to give seven days notice of a strike, raising the threat of industrial action across the country by the end of the month, just two years after the last national stoppage.

Deputy general secretary Dave Ward said: “This is a huge vote of no confidence in Royal Mail management. The company has tried to make out that problems only exist in some local offices, but postal workers across the UK have now spoken and they say no to Royal Mail’s arrogance.”

Earlier yesterday, Royal Mail’s operations director Paul Tolhurst said a national strike would be “very damaging” and would hurt customers.

Robert Hammond, post expert at Consumer Focus, said: “It’s hugely disappointing to watch a great UK institution tear itself apart.

“We call on Royal Mail and the Communication Workers Union to urgently ask for Acas intervention to resolve this dispute.”

The decision could bring deliveries to a halt across the country. The network is already struggling to cope after a series of regional strikes has left millions of letters undelivered.

The strike could start as soon as next week and last for several days, throwing the postal system into further chaos. The union claims that as many as 30 million letters, cheques and documents have already been delayed by a series of local post strikes in the past few weeks.

In a further blow to Royal Mail, the online retailer Amazon, its second largest customer, said it was making contingency plans to use a rival service in the event of a strike.

The last national postal strike in October 2007, left an estimated 200 million letters and parcels caught in the backlog.

The recent regional strikes have left thousands of families and businesses facing bank penalty charges for late bill payments and threaten to disrupt the secondary school admissions process.