The stark warning comes from the House of Lords European Union Committee in a report calling on the Government to look urgently at measures needed to maintain security of supply as the UK becomes a net importer of gas.

The peers say they are not convinced by assurances from ministers and the energy regulator Ofgem that the UK has enough gas to meet severe peak demand between now and 2007, when interconnectors from Norway and the Netherlands come on stream.

Lord Woolmer of Leeds, the chairman of the committee, said: "While the minister for Energy, Stephen Timms, tried to reassure the committee, we remain unconvinced. Ofgem believes supplies are adequate except in extreme conditions. It is the extreme conditions we worry about."

National Grid Transco, the operator of the UK's gas and electricity transmission networks, is legally obliged to make its systems robust enough to meet the kind of peak demand for gas that occurs only once every 20 years.

The peers say they have no concerns about the company's physical capacity to cope with a huge surge in demand but are worried about whether there is sufficient capacity in the pipelines which bring gas into the UK. The report also calls on the Government to give reassurances that a terrorist attack on either of the UK's import terminals, at St Fergus in Scotland and Bacton in Norfolk, would not trigger a national emergency.

By 2010, the UK will import around 50 per cent of its gas, rising to 70 per cent by 2020. Demand will be met by the new pipelines linking the UK to the Netherlands and Norway.

The committee said that in the intervening winters, and even afterwards, it was not clear that the market-based "just-in-time" system for ensuring sufficient supplies would be adequate. Too much reliance, it added, was being placed on the ability of shippers to interrupt supplies to large industrial users and the effect that higher gas prices would have on demand.

The report concludes that the UK will be vulnerable to "low probability/high impact" shock to supplies for much of the next 20 years.

The committee calls on the Government to review its emergency procedures for handling a sudden and major loss of gas and consider introducing contingency arrangements to ensure "fast-track" reconnection.

An Ofgem spokesman said NGT had assured it there were adequate supplies to meet demand even in the event of a 1-in-50 style Siberian winter. The Zeebrugge interconnector was being upgraded and an import terminal for liquified natural gas would open in Kent next year.