Labour’s plan to take the National Grid back into public ownership would harm the UK’s switch to green energy, the grid’s chief executive has said. John Pettigrew said renationalisation was “the last thing the industry needs” as it invests to accommodate more wind and solar power on the UK’s power grids.

“Clearly, on nationalisation, we do not think it is a good idea,” Pettigrew said, as the company reported operating profits up 14% to £4.7bn for 2016-17. Its market capitalisation is about £38bn, including its US business.

“To spend tens of billions of taxpayer money on nationalisation I’m just not convinced would be in the interest of taxpayers nor of energy consumers going forward,” he told the Guardian.

Labour’s manifesto promised to take energy back into public ownership in order to deliver more renewable energy and cut costs for consumers. But Pettigrew said the grid had coped with the rapid growth in variable power from windfarms and solar panels in the past five years, and argued that such technologies would be hit by instability from the party’s proposal.

“What industry needs to take advantage of all these clean energies is stable regulation and stable policies,” he said. “The last thing they need is renationalisation.”

A Labour spokesperson said: “Britain is going backwards in low-carbon energy and infrastructure. Our national and regional grids are outdated, and are failing to incorporate renewable energy sources quickly enough. Nor are they investing in a smarter grid able to balance more volatile sources of renewable energy and deliver flexible capacity.”

Pettigrew, who joined National Grid shortly after it was privatised in 1990, said the costs of transmitting power across the UK had come down 40% since public ownership. Private companies would be better suited than the public sector to paying the £230bn-£462bn annual investment needed globally to switch to clean energy, he claimed, citing a figure from a recent report.

National Grid spent a record £4.5bn on capital expenditure for its UK and US businesses last year, up from £3.9bn for the previous financial year. Analysts broadly welcomed the company’s “solid” performance and profits on Thursday, which were slightly above expectations.

“For those wanting a reliable income from their investments, National Grid can’t be far from the top of the list,” said George Salmon, equity analyst at investment adviser Hargreaves Lansdown.

Separately, investors in two of the UK’s biggest energy companies appear to have shrugged off the impact of Theresa May’s price cap on the energy bills. The share price of British Gas owner Centrica was up by 2% and SSE was up 1% on Thursday after the Tory manifesto included only a woolly promise to protect “more customers on the poorest-value tariffs”, compared with the 17m households the party had pledged before.

The Conservatives also said they would remove the need for planning permission for companies undertaking exploratory shale drilling, and create a new shale regulator to speed up development. With public opinion mostly against fracking, the local planning system has caused long delays for the industry, even after ministers attempted to fast-track the process, so the move would be a significant change.

Onshore windfarms, which the Tories campaigned hard against in the 2015 general election, were still considered unacceptable in England, but would get support in remote Scottish islands.

One notable omission was nuclear power, compared with the 2015 manifesto, which promised a “significant expansion in new nuclear”. “The lack of any mention of nuclear energy is telling: it’s clear May doesn’t want to be associated with a beleaguered industry at a time when alternatives like wind and solar are getting ever cheaper,” said Greenpeace UK’s executive director, John Sauven, who was also critical of the support for shale gas.

One right-leaning thinktank said the manifesto oversold the benefits of fracking. Sam Hall, a senior researcher for Bright Blue, said: “While stringently regulated fracking could meet the UK’s demand for gas for a couple more decades, the Conservatives’ priority should be incentivising cheap renewables, which are attracting the majority of new energy investment worldwide, as part of its modern industrial strategy.”