LONDON — After delaying a project to build a nuclear power plant with Chinese investment, Britain’s government on Thursday gave the go-ahead for the plant, but insisted on new conditions designed to protect the security of critical infrastructure.

The decision ended weeks of uncertainty that had strained relations with China, which is financing more than a third of the $23.7 billion power station, and with France, whose largely state-owned energy giant EDF is paying for the bulk of the project.

By pressing ahead with the Hinkley Point C nuclear power plant on the Somerset coast of England, Prime Minister Theresa May appears to be open to greater involvement by China in Britain’s energy industry. China also wants to build and operate a nuclear plant of its own design at another British site, at Bradwell-on-Sea, in Essex.

Mrs. May said in July that her government would not yet sign off on the Hinkley Point deal, reportedly on security and economic grounds, deciding instead to review the plans for the new power plant. It was one of her first big political moves after succeeding David Cameron as prime minister, and was seen as a sign that she was uncomfortable with some aspects of Mr. Cameron’s aggressive pursuit of an economic partnership with Beijing.