An MP said the creation of a group chief executive for two east London hospital trusts "further cements" her fears of a merger.
The new role will oversee Barking, Havering and Redbridge University Hospital NHS Trust (BHRUT), which runs Queen's Hospital in Romford and King George Hospital in Goodmayes, and Barts Health NHS Trust, which includes Royal London and Newham Hospitals among its cohort.
Former home secretary Jacqui Smith, chair in common of the two trusts, announced the move on Thursday (February 24).
Ms Smith said whoever was appointed would be responsible for developing collaboration further between the trusts.
But Dame Margaret Hodge, Barking MP, said she is concerned the announcement is a step closer to a merger.
She told this paper: "With the creation of a new chief executive role to lead both trusts, my fears have been further cemented.
"We all know what a step closer to a merger means - money being funnelled away from Queen's and King George to central London.
"This misguided strategy is a terrible mistake that could damage our vital local services. I will fight it every step of the way.”
The trusts declined to respond specifically to Dame Margaret's comments, but Ms Smith told a joint health committee meeting of councils in December that there was no plan for a "mega merger".
The creation of the new role follows an announcement that Barts chief executive Alwen Williams will be stepping down later this year.
She has spent almost seven years in the position and more than 40 years in the NHS.
Ms Smith said Ms Williams' impending departure presented "both a challenge and an opportunity" for the NHS in east London.
On the group chief executive role, she added: "It will enable us to play a key role in the health system across north east London; to work effectively with partners in local government in tackling health inequalities; and to be a strong voice for our patients and their communities."
BHRUT said in December that more than 1,500 Barts Health patients were having scans and procedures through its services where there was spare capacity, with clinicians and managers from Barts helping BHRUT in areas such as emergency care.
Matthew Trainer, BHRUT chief executive, will remain responsible for running Queen's and King George, but the group chief executive will be the "accountable officer" for both trusts.
Mr Trainer said: “It’s been a privilege working alongside Alwen. I believe the plans we’ve produced for her successor will ensure our two organisations continue to work together and improve."
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