Theresa May deserves credit for delivering, on Thursday, the first domestic speech dedicated to the environment by an occupant of 10 Downing Street for 15 years. But lavish accolades are sure to be withheld, pending evidence that action will match rhetoric. Mrs May argued that ecology is central to Conservative philosophy, which she characterised as the ethos of nurturing a natural inheritance from past generations and bequeathing it safely to future generations. She cited Disraeli’s River Pollution Prevention Act, the 1956 Clean Air Act and Margaret Thatcher’s action to protect the Earth’s ozone layer in the 1980s.

Those are valid points. But the story turned tendentious when it reached David Cameron, who, according to Mrs May, “restored environmentalism to a central place in the Conservative agenda”. He did no such thing. Mr Cameron embraced green issues in opposition to signal culture change in a party that had lost touch with the electorate. Once in office, he lost interest. His government fell laughably short of its pledge to be “the greenest ever”. If Mrs May was personally disappointed, she said nothing at the time.

On taking over the Tory leadership, she distanced herself from Mr Cameron’s “modernisation” project – of which greenery had been the emblem. Yet now she resurrects the theme. A strong influence on that decision comes from Michael Gove, who has earned proximity to the new leader after serving time in post-Cameron banishment. Mr Gove has been energetic in pursuit of eco-friendly causes: banning plastic microbeads in cosmetics; restricting neonicotinoids that harm bees; phasing out diesel engines. Mr Gove has also insisted that Brexit will not lead to a dilution of environmental standards.

Much of this week’s rhetoric from the prime minister has been prefigured in speeches by her environment secretary. There was not a lot of new substance. This supports the view, aired on Thursday by a former Downing Street communications adviser, that the government’s “25-year plan” for the environment was originally conceived as a minor initiative and only later upgraded in panic at the Tories’ loss of popularity among voters who care about such things. The prime minister spoke with moral urgency about the “scourge” of waste. And yet the action she proposes is timid. The most concrete proposal is an extension of the existing charge for using disposable plastic bags.

Beyond that, the government will work with supermarkets “to explore introducing plastic-free aisles”. Manufacturers will be “encouraged” to “take responsibility for the impacts of their products”. There will be a “call for evidence” to explore a tax on other single-use plastics. Mrs May spoke encouragingly of a transition to renewable energy as part of global efforts to combat climate change. But she added nothing significant to the policy portfolio on that front. With a working horizon of 25 years, the ambition should have been greater.

In 1961, the US President John F Kennedy pledged to put a man on the moon within a decade. Mrs May’s self-imposed deadline for ending plastic waste is 2042, by which time she will not be prime minister. Therein lies a flaw in the plan. It is long on aspiration, short on targets and enforcement. There is no sanction for politicians or businesses who fail to do their bit. Mrs May calls on her audience to trust the Tories to care for the environment on the basis that their philosophy recommends it. Indeed it does. But that is not sufficient cause to believe that a government with so many other conflicting imperatives will make good its green promises.

Still, the very existence of the speech testifies to the power of public pressure to force the environment up the political agenda. It is surely better that the prime minister responds to that pressure with some ambition than with none. She has set an unambiguous moral test for herself and her party. The cost of failure, politically and environmentally, will be high.