Labour and Conservative leaders of two contrasting areas have pledged to put their political differences and separate challenges aside to work harmoniously at the launch of the country’s first city-rural combined authority.

There was standing room only at York’s 15th Century Guildhall as City of York and North Yorkshire council leaders Claire Douglas and Carl Les branded the first day of the York and North Yorkshire Combined Authority, the vehicle for devolved power from Westminster, “momentous”.

The body, which will be headed by a mayor following an election on May 2, will be England’s first in England to have responsibility for a fire and rescue service, and will also govern the police service.

The event heralding the body, which will take responsibility for strategic improvements to the region in areas such as housing, the economy and transport, had been compromised as Cllr Les could not deliver his prepared speech as he was delayed by severe congestion on the outskirts of the city.

Filling in for Cllr Les, Richard Flinton, North Yorkshire Council’s chief executive, said the combined authority’s launch signified the first truly rural and city devolution deal, binding the two distinct areas together.

He emphasised that with £18m a year in extra Government funding over 30 years to invest in local priorities the councils had negotiated a “really strong deal” compared to others that have been achieved across the county.

He told the Guildhall there would be “some difficult and testing conversations” between Labour-run York and Conservative-run North Yorkshire councils, but that “collective endeavour” would be the combined authority’s “guiding star”.

Mr Flinton said: “It is absolutely crucial that we stay working together as a city and a county.”

Cllr Douglas’ “region before politics” speech underlined the “tremendous importance that we stick together as a team” and work for the benefit of more than 800,000 residents.

She said she had already “built a respectful and productive partnership” with North Yorkshire’s leadership to tackle the biggest challenges facing the region, including housing, transport and cutting carbon emissions.

She concluded: “Let’s get on with it.”

After the speeches, when asked how the politically split combined authority would work together, Cllr Douglas said: “Even though we have got quite different politics and challenges we have got clear threads that run through the challenges of York and North Yorkshire, such as affordable housing and getting around efficiently.”

Cllr Les added: “We will cooperate about spending more money that is coming into the region. You cannot deny that there will be political differences, but actually, those differences will come out in the election for the mayor – we will be tribal in that – but once the mayor is elected we will come together to deliver improved services for the people we both represent.”