DEEP concerns have been raised that the Royal Mail's six-day a week universal service obligation (USO) to Scotland and the rest of the UK is under threat from increased competition.

Royal Mail's 21 per cent fall in its six-month operating profit to £279m was less severe than many analysts had predicted but there was a warning that online retailer Amazon's delivery service would more than halve the growth potential for the parcel business of the former state-owned company.

Twelve months on from its controversial flotation, Royal Mail shares stand at about 430p, having slumped eight per cent in the past 24 hours and by 30 per cent from their February peak.

The firm has argued rivals are able to cherry-pick the services it offers, putting the USO at risk.

Moya Greene, the Royal Mail's chief executive, pointed to the problem of unfettered direct delivery competition, saying there was an "urgent need for a new framework that will secure the sustainable provision of the universal service for the future".

No 10 sought to play down fears about the USO, making clear the changes to the Royal Mail, which had been haemorrhaging millions of pounds a year, were made to make it a successful company and that ensuring this was the case would guarantee the universal service.

Ofcom, the industry regulator, also emphasised how protecting the USO was at the heart of its work.

But Chuka Umunna for Labour said it was clear the Government's "fire sale" of Royal Mail was putting the universal service at risk and called on ministers "to give assurances on the future of Royal Mail's services and what action they will be taking to defend the USO".

Mike Weir for the SNP said it was "painfully clear the UK government should never have sold off a valuable public asset at well below its true value and despite all the warnings about the end of the USO".

He added: "We know the majority of Scots were opposed to the privatisation of Royal Mail; more than any other part of the UK. We need a postal service that meets the needs of our communities and one which is brought back into public ownership."