It also appeared to be an attempt to find friendly turf even as May struggles on many other political fronts, including trying to hammer out a deal to break from the European Union. But that didn't stop critics from portraying the move as a bid to rebrand a gasping Conservative Party.
In a speech at a nature reserve in southwest London, May said that her Conservative government's environmental agenda was now "center stage" and that "conservatism and conservation are natural allies."
She also focused part of her speech on the "scourge" of plastics and pledged to eliminate what she called "all avoidable" plastic waste by 2042.
"In years to come, I think people will be shocked at how today we allow so much plastic to be produced needlessly," she said in the first major environmental speech by a sitting British prime minister in 14 years.
Plastic pollution has become a talking point among environmentalists around the world. Some countries — from impoverished Bangladesh to wealthy Germany — have imposed bans on plastic bags or mandatory fees for their use.
The most-watched television program in Britain last year was David Attenborough's "Blue Planet II," which highlighted the devastating impacts of plastics on marine life, showing footage of albatrosses feeding their chicks plastic bags and food packaging.
May paid tribute to Attenborough's work, saying his BBC documentary had opened the eyes of millions of viewers.
Opposition politicians said the plan was a cynical ploy to try to lure young, eco-conscious voters to the Conservative Party, many of whom voted for Labour in the last general election. Polling commissioned by Bright Blue, a center-right think tank, found that climate change was the top policy issue for Britons age 18 to 28.
Katie Perrior, May's former director of communications, said May's enthusiasm for the environment, while perhaps genuine, is rather new.
Writing in the Times of London, Perrior noted that Andrea Leadsom, the former environment secretary, was once told to make the 25-year plan "as boring as possible."
Now, she said, "the tables have turned."
May said the moment was right to outline Britain's long-term vision as it heads toward the E.U.'s exit door next year. For decades, the bloc has not only set many environmental standards but has also policed them, with the power to fine violators.
"Brexit will not mean a lowering of environmental standards," May said.
One of the most eye-catching elements of the plan is an effort to encourage supermarkets to offer "plastic-free aisles," with food either loose or in nonplastic packaging. She also seeks to extend the 5-pence charge on plastic bags (about 7 cents) to small retailers who are currently exempt. The charge currently applies to shops and chains in England with 250 or more employees.
Some environmental groups applauded the government for shining a spotlight on environmental issues but said the plan did not go far enough.
"It's brilliant in symbolic terms that a sitting prime minister is saying that the U.K. needs to be clean and green. But there are many things we could be doing today, like introducing a bottle deposit return scheme," said Dustin Benton, policy director at Green Alliance, an environmental think tank. He said the last prime minister to deliver a major speech like this was Tony Blair in 2004.
He also said the British government needs to introduce legal commitments, not just outlines and proposals. "As we leave E.U., people in the U.K. need the same rights to hold the government to account," he said.
Many commentators noted that the plan was broad-brush and short on specific action. For instance, it was unclear how exactly the British government would "encourage" supermarkets to offer plastic-free aisles.
This is not the first time the Conservative Party has tried to upgrade its eco-credentials. May's predecessor, David Cameron, promised to run Britain's greenest government and was photographed hugging a husky in the Arctic before he came to power.
In her speech, May paid tribute to Cameron for restoring environmentalism to a "central place in the Conservative agenda" and spoke of the changes she has made to her own life.
She referred to her love for walking, said she regularly recycles and noted she has a barn owl, bat and bird boxes in her garden.
"So we are trying to do our little bit there as well," she said.