The £6 annual "broadband tax" has been labelled as a backwards step for the industry by two leading internet service providers (ISPs).

Under the plans, revealed in the government's Digital Britain report on June 16th, all households and businesses will pay 50p a month on their fixed telephone lines to help fund the rollout of next-generation fibre broadband networks.

However, Charles Dunstone, Chief Executive of TalkTalk owner the Carphone Warehouse, told the Sunday Times: "It is like a poll tax, a fixed figure for everyone. I don't really know if the government can justify it to the electorate."

Jeremy Darroch, head of Sky Broadband parent company BskyB, also warned that a stealth tax could hurt competition between telecoms suppliers and drive prices up.

Speaking to the newspaper, he added: "There are hard-pressed people who see a phone line as a necessity but may have no interest in broadband."

Last week, Forrester Research analyst Ian Fogg claimed that the tax will only be able to raise an annual sum in the "low hundreds of millions" from the UK's 34 million fixed telephone lines, which is some way short of the amount required to establish a nationwide fibre broadband network.

BT and Virgin Media are expected to be the biggest beneficiaries of the broadband tax.