The Government seemed to be "crossing its fingers" that private firms would deliver reactors on time and budget, despite delays and cost overruns in other countries, the Energy and Climate Change Committee chairman Tim Yeo said.
A report by the committee raised concerns there was no "plan B" for the energy sector if the planned series of reactors were not delivered on time.
But Mr Yeo also warned any such contingency plan, which would rely on a step change in energy efficiency measures or an even greater reliance on renewables, was difficult to deliver.
Government climate advisers have said the electricity sector needs to be largely decarbonised by 2030 if the UK is to be on track to meet legally-binding targets to reduce carbon emissions by 80% on 1990 levels by 2050. However, all but one of the UK's nuclear plants are to close by 2023, and while there are plans for a new fleet, MPs had been told the proposals were "ambitious at best and unrealistic at worst".
"If new nuclear power stations are not built on time our legally binding climate change targets will be extremely challenging and much more expensive to build," Mr Yeo said. "The Government seems to be crossing its fingers that private companies will deliver a fleet of new nuclear power stations on time and on budget. Ministers need to urgently come up with a contingency plan."