Royal Mail employees have been praised as a report finds that more than nine out of ten letters are delivered on time, the best figure for five years.

However, the findings come at a difficult time for the Royal Mail, as workers began voting on strike action on Thursday, after talks between bosses and the Communications Workers Union ended without agreement.

"Our people are working hard to continue driving the results in the right direction," said chief executive Adam Crozier.

"The latest figures show that their efforts for our customers are paying off."

However, he warned that such improvements would be "thrown away" by workers staging industrial action.

Workers have been offered a 14.5 per cent pay deal over 18 months, say Royal Mail bosses.

But that figure is disputed by the trade union. Officials argue the only guaranteed portion is a three per cent rise from October and a 1.5 per cent increase in April, both of which come with too many strings attached.

Royal Mail chairman, Allan Leighton, has written to staff members asking them not to back strike action.

"If you vote with the activists amongst the union against the deal - or don't vote at all - we begin the process of commercial suicide," he wrote.

The company wants to cut as many as 30,000 and scrap the second daily post in a bid to reduce its £750,000 daily losses.

Union bosses denied they were obstructing any deal between the two sides.

"It's quite clear that [the Royal Mail] came here with no intention of negotiating sensibly whatsoever and we will continue with our ballot on that basis," said spokesman Ray Ellis.

"They've treated the union with absolute contempt. We remain prepared to negotiate seriously when the business is prepared to do so."