The Prime Minister has been accused of "ducking" concerns about the future of a planned multibillion-pound nuclear power station following huge losses reported by one of its backers.
NuGen, the company behind the Moorside scheme in Cumbria, has insisted that Toshiba remains committed to the project despite doubts after the Japanese giant revealed it was on track for losses of 390 billion yen (£2.7 billion) for the year to March.
Toshiba has a 60% stake in NuGen.
Theresa May was asked about the project during a visit to Copeland in Cumbria, ahead of next week's by-election in the constituency.
She said: "The consortium involved in Moorside has been absolutely clear. They have reconfirmed their commitment to Moorside.
"The Business Secretary Greg Clark has spoken to NuGen and Toshiba in the last few days and, in fact, over the last six months, he has made three visits to Japan, working with the government there and businesses there about their investment here in the UK.
"It is the Conservatives who are committed to the nuclear industry in the UK. We have agreed the first new nuclear build in a generation here in the United Kingdom.
"We recognise - and Trudy Harrison, our candidate here in Copeland, has made very clear to me - the importance of Moorside and the importance of the nuclear industry.
"Jeremy Corbyn was asked five times in one interview whether he would back Moorside and he would not back Moorside.
"It's the Conservatives who understand the importance of the nuclear industry. Trudy Harrison knows that, her husband works in the nuclear industry. She knows how important it is."
Justin Bowden, national officer of the GMB union, which represents nuclear workers, said: "Theresa May has ducked the central question, just when strong leadership was required.
"It is crucial for the future of Moorside, for the economy and jobs in Copeland and for the future security of Britain's electricity supply that there is a Government-backed Plan B.
"The Government just crossing its fingers and toes will not guarantee the lights stay on if there is a further wobble with Toshiba."
A hustings is being held in the constituency later which is expected to feature questions from nuclear workers and their families about the future of Moorside.