Labour mayor Dr Nik Johnson has come under fire from a union official for appointing a Conservative as his deputy.

He appointed the leader of Peterborough City Council, Conservative Wayne Fitzgerald, to the role of statutory deputy mayor of the combined authority.

Dr Johnson believes a “successful combined authority is one that collaborates across traditional political divides”.

But James Youd, secretary of Cambridge Unite the Union Community Branch and Labour campaign organiser, criticised the decision.

He said the deputy role should not have gone to a Conservative.

He also said that the only other Labour councillor on the board, Lewis Herbert, did not want the role but that it should have been given to a Labour councillor, possibly from the city council.

Under the constitution, the statutory deputy mayor role must be held by a board member.

Mr Youd said: “What I think is very regrettable is that Dr Nik has chosen a Conservative rather than a member of his own party.

“I am also very doubtful as to whether that will have any good ends- it will probably end in failure.”

Mr Youd added: “As a hardworking organiser in the city of Cambridge Labour Party what we need more than ever is Labour working at a city level at a county level and in the combined authority, but I’m not sure that the current direction of the mayor merits that to be honest.

“I’m doubtful of the ability of the mayor to deliver what he says while ensconced with a deputy who is a Conservative.”

He added: “I did not vote for a Conservative mayor indeed, Dr Nik has ensured that we have a Labour mayor, now he must live up to the expectations of being a Labour mayor unshackled from the various people on the combined authority that may not wish him well.

“No doubt the Conservatives on the combined authority don’t.”

He said he is “not only sorry but embarrassed” that a Conservative was chosen, describing the decision as “wrong”, and saying “Nik didn’t stand as an independent he stood for the Labour party”.

Dr Johnson responded: “Following the recent election the political make-up of the combined authority is complex and finely balanced.

“If we are to do things better and achieve the co-operation I campaigned on for the benefit of all residents we have to work together across party lines.

“However, there is no formal coalition or power sharing agreement just a simple recognition that if we are to move forward, we need to work together collaboratively.”

Leader of Cambridge City Council and combined authority board member, Lewis Herbert, said he was not asked to be deputy mayor but said: “I was happy to do the housing portfolio and I didn’t feel that I had the time to be deputy mayor.”

The combined authority’s decision-making board is currently occupied by four Conservatives, two Liberal Democrats one of whom is from the joint administration on the county council and so has a Labour substitute.

Labour has two full-time members in the mayor and the leader of the city council, and the apolitical chair of the business board makes up the ninth vote.

Dr Johnson said: “One thing which unites all the leaders of the councils which make up the combined authority is a passion for the areas they represent, and none more so than Cllr Fitzgerald.”

His new deputy said: “We will not realise our region’s potential to level up – to reduce inequalities and increase opportunities and quality of life – if we do not all come together to use our combined energies and talents to make it happen.”

“All involved have a big job ahead of us to improve the health and wellbeing outcomes for people and hopefully at the same time reduce inequalities across the whole of Cambridgeshire.”

He added: “I want to see the university come to fruition and continue our investment in affordable housing, innovative transport schemes and infrastructure along with our culture and leisure offerings.”