A minimum 40% plunge in Europe’s CO2 emissions by 2030 agreed by EU leaders last week was a “historic moment” on the road to a global climate deal, enabled by a new British relationship with Poland, the energy minister Ed Davey has told the Guardian.

The bloc’s proposed greenhouse gas curb will be studied closely by China, the US and other major emitters ahead of a global climate summit in Paris next year that aims to agree on the first new emissions-cutting treaty since the Kyoto protocol in 1997.

“I really think this package is quite a historic moment on the pathway to that elusive global deal,” Davey said in an exclusive interview. “It is probably the most significant environmental agreement that a British government has ever been involved in.”

Coal-dependent Poland had threatened to veto any agreement that raised its energy prices – adding to the country’s ‘renegade’ image in Brussels. But in lengthy talks, the Polish environment minister, Marcin Korolec, was persuaded by the UK’s agenda of an energy transition that was cost-effective, flexible, technology-neutral and secure.

“We spent more time with Polish ministers, officials and their energy sector than any other country – just to understand where they’re coming from because you have to respect other member states and find a way forward,” Davey said. “It was painstaking and took a protracted amount of time but it was worth it in the end.”

The agreement allows the EU to continue pursuing a roadmap that is intended to arrive at a reduction of carbon output of 80-95% by 2050, in line with IPCC recommendations for keeping within a 2C trajectory of global warming.

Asked whether Poland was committed to that end goal, Davey said: “I think they are. I think they see it as in their interests for energy security reasons.”

Polish government sources though, hedged when asked the same question. “There is no 2050 goal,” one said. “There is only 2030.”

The 2030 package has been criticised for granting Poland concessions including an estimated 200 million free carbon allowances (emissions credits) – worth about €4bn (£3bn) at a carbon price of €20 per tonne – and a new modernisation fund for poorer EU countries to upgrade their energy sector, which may be worth €6bn in the decade to 2030. Environmentalists fear that some of the fund could be spent on Polish coal-fired plants.

From the Polish perspective, indigenous coal supplies offer immediate energy security in the face of an often hostile neighbour to the east.

Davey said that the final deal had a “greater environmental integrity” than the 2020 climate package negotiated by Tony Blair, because it would give fewer free allowances to Polish coal plants. “Of course we were never going to get a deal with Poland if they weren’t able to burn more coal than possibly we were comfortable with,” he added.

“We had the UK on our side in many issues,” a Polish official confirmed. “The [Paris 2015] review clause was one of these. That helped. Apart from that, good working relations between Poland and the UK also helped when closing the deal.”

The review clause is an ambiguously worded text, promising to “revert” to the EU’s package after the Paris summit. EU leaders insist that the preceding passage in the text calling for ambitious counter-pledges from other states indicates that the 40% greenhouse gas cut may only get added to.

“The package is clear that it is ‘at least 40%’ – so the review is upwards only,” Davey said. “If we get a really good deal and America and China step forward, it means that we can go further. But the EU is saying that we are going to do 40% regardless of the rest of world.”

Warsaw attaches a different emphasis to the clause, related to the way that increased ambition may be imposed outside the bloc’s carbon market, but touching on the fractious arguments over qualified majority voting and, potentially, the national veto.

“The review clause and embedded ‘consensus’ are there to make sure the spirit of the conclusions is reflected when implementing the package,” a government source said, “so there is no ‘upwards-downwards’ discussion but [rather] how to make sure everyone feels safe with us further moving forward.”

This may set alarm bells ringing for environmental NGOs and clean energy industries, which have already condemned the package for a lack of legally-binding targets.

Friends of the Earth say that even the aspirational 27% improvement in efficiency by 2030 will be based on a projection made in 2007 before the economic crisis, when expected growth rates – and thus energy consumption – were far higher.

Ingrid Holmes, the associate director of the E3G thinktank told the Guardian that 2007 was the “worst possible” starting point for energy use reductions. “It’s before the slowdown so overestimates energy use compared to what we are doing,” she said. “It equals 12% energy savings in today’s economy.”