A campaign has been launched against privatisation of Royal Mail, which supporters fear could end the obligation to charge the same for postal services throughout the UK and bring in a £1 stamp.

The Save Our Royal Mail campaigners claim the countryside would be left isolated.

And they fear that, as it costs more than the price of a stamp to deliver to a rural address, the Universal Service Obligation would be at risk.

They also say that, despite assurances to the contrary, the postal services regulator Ofcom is working to determine the real cost of deliveries to rural areas. Campaigners fear stamp prices would shoot up if they are no longer regulated and VAT may eventually apply.

In a statement, the campaigners said: "Small businesses will suffer. For many small businesses, especially those in rural areas, there is often no alternative to the Royal Mail. Suffering from high energy bills, businesses can ill-afford to see the cost of using the postal service rocket."

A website has been set up offering to email a letter to MPs and the chance to sign the campaign's petition.

Campaign director Mario Dunn said: "We have learnt the prospectus group within the Royal Mail are working feverishly and people in the know in banks and the city have said that a potential initial public offering is being lined up for September.

"It will mean that a certain percentage of Royal Mail will be offered up to investors."

He added: "We want to take our message to the politicians: do not rush headlong into a sell-off if you cannot guarantee a privatised Royal Mail will constrain its prices and provide these services at their current level."

Ofcom said it had no powers to dismantle the USO or cut rural services.

Meanwhile, a Royal Mail spokesman said it was "pure speculation" to suggest that stamp prices could reach £1 in the next few years.