The telecoms regulator is exploring the potential for putting fibre-optic cables into sewers and existing communication ducts.

Ofcom hopes that its survey of underground infrastructure will prove to telecoms companies that deploying next-generation broadband networks – providing speeds of up to 100 megabits per second or more – will not be as expensive as they fear.

“Super-fast broadband – next-generation access and networks – are crucial to the UK’s future,” Ed Richards, Ofcom chief executive, was due to say in a speech on Wednesday night. “We must prepare now.”

Mr Richards said more broadband customers were realising that advertised broadband speeds “may be a far cry” from experience. Investment at all levels of the communications network will be required to meet consumers’ demand for bandwidth-intensive services such as video, he said.

Analysts’ estimates of the cost of deploying a UK-wide fibre network have ranged between £4bn ($7bn) and £15bn ($29bn), depending on whether cables will run only to local exchanges or into every home. Ofcom said 70-80 per cent of the cost of deploying such networks went on civil works to lay cables underground.

The regulator’s survey has been inspired by rapid progress on fibre deployment in Paris, where three rival broadband providers are installing fibre networks. However, work in France on using existing underground infrastructure was “still very localised”, with the cost of accessing sewers and the density of customers in Paris more favourable than in London, according to Matt Yardley of researchers Analysys.

The UK’s telecoms ducts are largely owned by BT, installed when it was a publicly owned monopoly. Alongside any physical survey, use of these ducts would therefore require detailed commercial negotiations. These could be even more complicated than the settlement on local loop unbundling, which enabled other communications suppliers’ equipment to be installed in BT exchanges, Mr Yardley said.

“Ofcom’s previous consultations have not found any demand for this in the UK,” BT said, adding that it believed the wholesale model was “serving consumers and industry well”. “We have an open-mind on duct-sharing though there are some practical operational issues associated with it.”

Martin Mabbutt, analyst at Nomura Securities, said the idea of using existing underground infrastructure was well-established . But a sample survey might not reveal all the complications of localised fibre deployments – sharp corners, for instance, create difficulties for most fibre cables. “You won’t know until you get down the hole.”