The country's biggest mobile operator Everything Everywhere plans to begin an auction of wavelength spectrum next month, the Financial Times reported on Tuesday.

The newspaper cited people familiar with the plan as saying Everything Everywhere is in discussions to appoint Royal Bank of Scotland to oversee the process.

The sale mandate of the mobile operator is expected to be confirmed next week, with plans to begin the sale shortly afterwards, the FT said in the piece published on its website.

The sale could raise as much as 400 million pounds, but the exact price of the sale is difficult to gauge, said one source cited by the FT.

The group is a joint venture between France Telecom and Deutsche Telekom and runs the UK's Orange and T-Mobile brands.

Everything Everywhere has been forced to sell some of its spectrum by European competition authorities after the merger of Orange and T-Mobile to create Britain's largest mobile operator by subscribers.

(Reporting by Stephen Mangan; Editing by Bernard Orr)