A Whipps Cross Hospital campaigner has lost her appeal against dismissal for serious misconduct.

Charlotte Monro, chairwoman for Unison’s Waltham Forest health branch, was dismissed from the Leytonstone hospital in October after 26 years of employment.

She previously claimed that she was sacked because of her union work.

Barts Health NHS Trust, which operates Whipps Cross, says she was dismissed for failing to disclose previous criminal convictions and breaching confidentiality.

A third charge, that of deliberately misrepresenting in a negative manner the trust’s future intentions for its stroke services, was not upheld on appeal.

“We would like to stress, categorically, that the reasons for Ms Monro’s dismissal were for personal misconduct and not as a result of her union role,” a spokeswoman said.

The trust says the breach in confidentiality allegation relates to unauthorised dissemination of pre-consultation information, outside her union role, without approval and before content had been ratified.

It is claimed this led to “misinformation, unnecessary confusion and anxiety” among staff.

Ms Monro was described in 2009 as “one of Whipps Cross’ greatest champions” by the hospital’s then chief executive.

She was honoured for her work in a campaign to save the hospital after the government considered an option to downgrade Whipps from a district general hospital.

The spokeswoman added: “Barts Health NHS Trust’s priority at all times is the safety of its patients, and we therefore had no alternative but to take action against Ms Monro in relation to her failure to disclose to the trust multiple previous criminal convictions – two of which resulted in prison sentences – including for violence.”

Ms Monro failed to declare these convictions on more than one occasion both to the trust and to her own professional body on numerous occasions, including as recently as September, Barts alleges.

Ms Monro is expected to issue a statement to the Guardian today.