Theresa May assures MPs Paris climate change deal will be ratified

And in a withering assessment of the Government, he said the UK has been "leapfrogged" by the world's two biggest polluters - the US and China - who have both signed off on the Paris pledge.

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Theresa May was challenged over her commitment to the deal in her first PMQs since the summer recess, but told the Commons: "I'm happy to give you the assurance that we will indeed be ratifying the Paris agreement."

Labour used its Opposition Day debate to press the matter, calling for ministers to set out an immediate timetable to ratify the pledge - the culmination of 20 years of negotiations which for the first time commits all countries to cut carbon emissions.

Shadow climate change minister Barry Gardiner urged the UK to "follow China and America's lead and get on and ratify this agreement".

Speaking during the debate, he said Britain has gone from leading the world in tackling global warming through its landmark 2008 Climate Change Act, which committed the Government to slash emissions by 80% of their 1990 levels by 2050, to sliding back on its commitments.

He said: "That is what we achieved here and it has become a model across the world, but we have to follow up, and the tragedy is that this Government has been backsliding from it."

Mr Gardiner said he offered to change the motion to make it the formal vote required by the House of Commons to ratify the Paris treaty, but said his "olive branch" did not receive a formal reply.

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He warned that abandoning or watering down the country's commitment to tackling climate change and fostering green energy will see Britain lose vital investment opportunities.

He told the Chamber: "We are locked in a low carbon race and we are losing.

"The reason I want us to get on and ratify is not because Paris is some sort of totemic environmental symbol, it's because political leadership sends a strong signal to attract investment.

"Those countries that have a clear policy framework are the ones who attract investment. Those countries who have a stable policy framework are the ones who attract investment. In the UK over the past few years we have had neither."

The MP for Brent North said the UK's leadership on climate change "has fallen on this Government's watch" and has been "leapfrogged by the world's biggest polluters".

And he accused the Government of "incompetence" over the Hinkley nuclear power plant, which Mrs May postponed approving in one of her first acts as Prime Minister.

Pausing for dramatic effect, Mr Gardiner said: "Nuclear, Hinkley, oh dear - dither, delay, incompetence.

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"An overpriced contract, a contract for Britons that will now cost the bill payer not the £6.1 billion originally calculated by the Government, but the £30 billion as now determined by the National Audit Office.

"This is a project which is already eight years delayed, which the Prime Minister has now thrown into chaos."

Nick Hurd, Minister for Climate Change and Industry, said all the countries in the EU had to ratify the agreement - hence the delays on the British side.

"We signed the agreement as part of the European Union. We negotiated together and, a point ignored in his speech, the convention is that we will ratify together," said Mr Hurd (Ruislip, Northwood and Pinner).

"I'm sure colleagues will understand the complexity of a process whereby so many different countries are going through their domestic processes of approval, most of which differ.

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"This understanding that we will ratify simultaneously, this means it has always been understood, and this has been confirmed to me by the most senior people involved in the negotiation process, that the EU was never expected to be at the vanguard of ratification.

"That, in part, explains why others have chosen to go first."

He added this convention made it "difficult" for the Government to set a timetable for ratifying the agreement, given the need to coordinate with other countries.

Mr Hurd added: "We will start our own process as soon as possible and although I can't confirm the exact timetable, because processes are not complete, we will decide and we will communicate that at the appropriate point."

This was challenged by Labour, though.

Mr Gardiner said that in March the European Council had underlined the need to ratify the agreement as soon as possible.

The EU planned on ratifying the agreement in December, Mr Gardiner added.

Fellow Labour MP Alan Whitehead (Southampton Test) added that the agreement had already been through its domestic processes in France.

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SNP spokesman for energy and climate change, Callum McCaig, said: "I listened carefully to what the minister was saying and I'm still slightly at a loss as to why we can't press on with this.

"As we say in the north east of Scotland, it might be time to 'nip on a wee bit', because this is important."

Former shadow energy minister Mr Whitehead also warned that efforts to tackle climate change would "end in tears" unless the new minister got a grip on the Treasury.

He said decisions to abolish policies such as the Green Deal, which offered loans for work to make homes better insulated, were evidence financial decisions took precedence over those on climate change.

"Where the minister has a particular problem here, in his responsibilities and indeed the responsibilities of the secretary of state, is what the effect has been of the flurry of policies that took place last year on the long-term considerations as far as climate change is concerned," said Mr Whitehead.

"I think we can point the finger in terms of what happened under the previous department of energy and climate change with some of those previous changes. That is squarely at the Treasury.

"We had, over a period of time, over the latter stages of the previous government and certainly in the first period of the present Government, an energy and climate change policy of the Treasury, and an energy and climate change policy of the department of energy and climate change.

"When there was a particular issue as far as those policies were concerned, let us guess who came out on top.

"Get on top of the Treasury as far as these issues are concerned, because if it is allowed to run, if the Treasury domination of energy and climate change policy, with what they think and apparently still think are the things you can do, regardless of the long-term climate consequences are concerned, then this will end in tears."

Labour MP Mary Creagh, who sits on the Environmental Audit Committee, warned that Britain is slipping in its commitment to tackling climate change.

She said transport gas emissions increased in 2014 and 2015 while cuts to funding for the green energy industry and consumers have been a major setback.

She added: "The US and China have worked together to ratify this agreement. As I say, they are getting a head start in this next innovation race - the decarbonisation of advanced economies.

"We are fortunate we have got the Climate Change Act, we are fortunate we have got that framework, and it is the basis for this new industrial revolution in sustainable technology."

The motion in Labour's Opposition Day debate called on the House to note the lack of progress in ratifying the climate change agreement, as well as to publish a timetable to complete this process by the end of 2016.

The motion was passed unopposed.