The chair of England's first public inquiry into mental health deaths has vowed to "seek out the truth" in spite of difficulties getting documents from the NHS.

The first key evidence sessions in the Lampard Inquiry, which is examining more than 2,000 deaths at NHS inpatient units in Essex between 2000 and 2023, have started in London.

Baroness Lampard said the hearing was "breaking new ground", and a number of Section 21 legal notices had been issued to NHS organisations to force them to submit evidence.

She said: "We will seek out the truth", adding she would not hesitate to use her legal powers "to the fullest extent necessary to compel the production of evidence where it's not provided."

Baroness Lampard said the inquiry was of "national significance" as it focussed on "the big critical concerns about what went wrong over almost a quarter of a century."

The Lampard Inquiry has entered its third phase, having heard evidence in September and November 2024.

Counsel to the inquiry, Nicholas Griffin KC, said: "We have been unimpressed with a significant number of requests for deadline extensions and the number of occasions where providers have not given the material expressly asked for."

He said there were problems with the condition of paper records, "missing documents" and providers, including private ones, sending information late.

Mr Griffin said it was a criminal offence to suppress, conceal, alter, or destroy relevant evidence and said providers should be properly resourced to respond to the inquiry which would not be delayed because of it.

So far, the inquiry has heard impact statements from about 80 families

The original government investigation into the deaths of inpatients stalled after only 11 out of 14,000 staff agreed to take part.

But Mr Griffin said the inquiry was still facing barriers in the flow of information.

He said the inquiry team had asked providers and regulators for a reassurance that they would not take action against staff if they provided information to the inquiry or failed to provide it in the past.

He said almost all, including the largest providers, declined to give such undertakings and said the inquiry was reflecting on what further steps to take.

Baroness Lampard will hear from care regulators, experts, and the chief executive of the Essex Partnership NHS University Trust (EPUT).

She said she would confront difficult topics "head on" and promised to keep those affected at the "heart of the inquiry," adding that she wanted to make "lasting, positive recommendations to improve mental healthcare" across England.

During her evidence to the inquiry, the mother of one patient, Melanie Leahy, described the  NHS unit her son Matthew, 20, died in as "hell on earth."

Ms Leahy, who campaigned for more than a decade for an inquiry was joined by fellow campaigners outside the hearing , said it was a real chance to get the truth.

She said: "It's been years of heartbreak, unanswered questions and fighting just to be heard. At Matthew's inquest, they [those in charge of EPUT] walked out of the back door and didn't speak to anybody, let's bring them out now."

Campaigners and lawyers acting for bereaved families have alleged mental health services are still unsafe.

It is understood the inquiry team has referred ongoing concerns to regulators.

Mr Griffin said they would be looking at what recent inquests and deaths may reveal about the extent to which the issues in Essex "are really being addressed."

He said associate professor from Nottingham Law School, Dr Emma Ireton, who has written a book on public inquires, would be producing a report to support the inquiry's work on maximising the chance of its recommendations being implemented.

EPUT chief executive, Paul Scott, has apologised for deaths under his trust's care. He said: "As the inquiry progresses, there will be many accounts of people who were much loved and missed over the past 24 years and I want to say how sorry I am for their loss."

Baroness Lampard is expected to produce her recommendations for change in 2027.