JIM Murphy has been accused of undermining the Royal Mail in the very week it warned it was being harmed by private providers by using a rival postal service to send out material for his Scottish Labour leadership campaign.

It has emerged that the MP for East Renfrewshire is using private Fife-based company First Post to distribute information to Labour members, even though last year Murphy attacked Westminster Coalition plans to privatise the Royal Mail.

First Post, which consolidates its clients' mail to get bulk discounts from Royal Mail, says it can save customers up to 40% on bills "thanks to the deregulation of the postal market".

Murphy's rivals for the leadership, MSPs Neil Findlay and Sarah Boyack, used the 30% taxpayer-owned Royal Mail for their mailshots.

Last week, the chief ­executive of Royal Mail warned private companies are ­undermining the Universal Service Obligation (USO).

Costing £7.2 billion a year, the USO obliges Royal Mail to provide a six-day-a-week delivery service across the UK at standard prices.

Moya Greene, chief executive of Royal Mail, told the House of Commons business select committee that direct delivery firms such as TNT Post (which recently rebranded itself as Whistl), were cherry-picking profitable urban routes and leaving expensive rural ones to Royal Mail.

"It makes the universal service unfinanceable and uneconomic," she told MPs, a remark later denounced as "scaremongering" by the Liberal Democrat Business Secretary Vince Cable.

Although First Post is a mail consolidator rather than a direct delivery rival to the Royal Mail, the union representing postal workers said it was disappointed Murphy had chosen to use the firm instead of supporting Royal Mail.

John Brown, Scottish regional secretary of the Communication Workers Union (CWU), which backed Findlay for leader, said: "We're disappointed that he [Murphy] has used a mail house when Royal Mail provide perfectly good services.

"Companies like First Post have always been there, but the fact there are far more of them now and far more people use them, is having a bad effect on Royal Mail's ability to provide a Universal Service Obligation at a price that's affordable. [Murphy] should have done better.

"If his rhetoric about supporting Royal Mail and trades unions is true then he should not be using organisations like this. I'm extremely disappointed, but it does not surprise me."

Last year, Murphy said: "Royal Mail is one of Britain's most cherished institutions and there is a strong national economic interest in the maintenance of the universal postal services which millions of businesses and individuals rely on."

A spokesman for Findlay's campaign said: "Neil's politics are built on the idea of fair pay and people having decent conditions at work.

"So we made a conscious decision to use Royal Mail as we know that they are a living wage employer with a recognised trade union."

A Murphy spokesman said: "Mr Murphy is a strong supporter of the Universal Service Obligation."