A legal letter suggests the dropping of charges against former Pike River Mine boss Peter Whittall was part of a deal agreed to by government officials in exchange for reparation to the families of the men killed in the 2010 explosion.

Twelve health and safety charges laid against Whittall were dropped in Christchurch District Court on December 12. It was also announced at that hearing there would be a $3.41 million payment to the families of the 29 men who died in the mine and the two survivors.

At the time, Judge Jane Farish stressed to media there had been no back-room deal. One of Whittall’s lawyers, Stacey Shortall, also said any suggestion the payment offer from the Pike River Coal Company and its directors and officers was in return for the charges being dropped was ‘‘absolutely wrong’’.

But in an October 16 letter, Whittall’s lawyer Stuart Grieve QC lays out a proposal to make available $3.41m to the Pike River families.

The letter, released exclusively to Fairfax Media, says that in ‘‘advance of the $3.41 million being made available, it is proposed [with precise terms to be agreed] that ... the Ministry will not proceed with the charges laid against Mr Whittall by advising the Court that no evidence will be offered in support of any of the charges.’’

The letter also raised number of inadequacies about the level of investigation and evidence collected by the Ministry of Business, Innovation and Employment (MBIE) to bring a case against Whittall.

Opposition labour spokesman Andrew Little believes the letter made it clear ‘‘Peter Whittall has bought himself justice’’.

‘‘The central condition of the whole thing was that money would be paid to the families – this is a deal.’’

He said what was not clear from the letter was why the charges were discharged rather than withdrawn – effectively preventing Whittall from ever facing charges again.

‘‘I think that was also part of the deal and that information hasn’t been disclosed.’’

Earlier this month, documents released by Labour Minister Simon Bridges’ office showed there was ‘‘particular concern’’ at the ‘‘legalities and propriety’’ of such a payment.

The documents confirmed some weight – albeit low – was given to the offer in relation to the decision to drop the charges, but it was also set against a low likelihood of conviction.

A briefing document to the minister also referred to a ‘‘without prejudice and confidential letter’’ written to crown solicitor Brent Stanaway by Mr Grieve. It is not known what that letter contained as it was to be distributed only among a select group of people involved with the decision.

Little said he believed the details of why the ministry allowed for the discharge of Mr Whittall would be in that document, and called on the minister to release it.

Bridges is overseas but his spokeswoman said the letter Fairfax Media obtained was ‘‘substantially the same as the letter Little is referring to’’.

‘‘The letter was originally written under legal privilege, but MBIE requested an open letter as it wanted these matters to be transparent and open to public scrutiny.’’

WorkSafe NZ chief executive Geoffrey Podger said the offer was not solicited by the ministry.

‘‘It arrived by Stuart Grieve, nobody asked if they were prepared to offer money – they offered money.

‘‘Very careful legal advice was taken as to whether it was proper to take this into account at all. We got clear legal advice that we should take it into account, and it was one, but only one, of that factors, and not the predominant factor in the decision that was taken.’’

Podger said he ‘‘absolutely refuted’’ Grieve’s claim the level of investigation was not adequate. ‘‘We take the view that a very good legal investigation was done by one of our most experienced officers. We do not accept these criticisms and I made that clear at the time.’’

He said that in his experience, most legal letters of this kind ‘‘invariably make that kind of suggestion’’

Council of Trade Unions president Helen Kelly said Whittall should have gone to trial.

"All New Zealanders should be seriously concerned about how the Crown dealt with a letter from Peter Whittall's lawyers some two months before he was discharged," she said, adding it was concerning the letter had only just come to light.

"The facts are clear - this mine was run in the most dangerous of manners. It exploded only one year after opening killing 29 much-loved men.

"Mr Whittall made several key decisions which a royal commission criticised in regards to safety at the mine.

"There needs to be scrutiny of this decision both in order for the families of Pike to get some justice but also to reassure all New Zealanders that justice in this country cannot be bought."