To ‘deadname' someone means to call a transgender person by their birth name when they have changed their name as part of their gender transition.
The employee, referred to as Miss AB, told Kingston council that she planned to transition eight months before she did in July 2020.
Kingston Council took two years to change the name and details of the claimant on her pension records, door pass and name on the staff directory after she transitioned.
Her work locker had a Post-It note on it with her previous name crossed out and new name written instead, an employment tribunal heard.
Following a dispute about street lighting that Miss AB felt was unsafe, bosses sent emails about her including derogatory language and accused her of a "hissing fit".
Following this, she was told not to have direct contact with councillors.
Miss AB’s subsequent complaints of unfair treatment and a ‘witch hunt’ against her following her transition were not investigated.
She was instead told to apologise.
The tribunal heard this had a significant impact on her mental health, leading her to take sick leave for six months before making a tribunal claim.
Miss AB was awarded £25,423 in compensation including £21,000 for injury to feelings.
Read more: Joanne Lockwood: My gender journey
Matt Jenkin, head of employment law at law firm Moorcrofts, said the case shows that dealing with gender reassignment and transgender issues in the workplace can be a complex task for employers.
He told HR magazine: “Employers should make sure that equal opportunities and anti-bullying and harassment policies are reviewed on a regular basis and kept up to date.
“In this case, the Council had failed to keep their dignity at work policy up to date in line with the Equality Act 2010.
“Secondly, employers should work with employees who transition to quickly identify how name changes should be dealt with.”