Bereaved families have been traumatised by "distressing and appalling delays" to inquest proceedings, a landmark inquiry heard.
The Lampard Inquiry is examining the deaths of more than 2,000 mental health patients who died under NHS care in Essex between 2000 and 2023.
Fiona Murphy KC told the hearing "institutional defensiveness" by health providers was hindering inquests and preventing families from getting closure.
Essex Partnership University NHS Foundation Trust (EPUT) has apologised to those affected.
The public inquiry is England's first into mental health deaths, with evidence being heard in London after previous sessions in September and November.
Ms Murphy told of the "horrendous" experiences that families she represented had during their loved ones' inquests.
She said there had been an "extraordinary and shocking number of deaths" in inpatient units in Essex.
"The families' experience has been…the death of loved ones falling under the radar and of distressing and at times appalling delays," she said.
The barrister accused EPUT of knowingly disrupting inquest proceedings by being defensive.
This included "unreasonably disputing" the relevance of an inquest, failing to provide evidence and delaying its disclosure.
Ms Murphy said: "There has also been shameful misrepresentation that lessons have been learned when they have not.
"These defensive behaviours cause real harm.
"They cause the retraumatisation of grieving families, they obstruct the truth, they obstruct lesson learning and they act as a fundamental bar and barrier to change."
