Contradicting Michael Howard's version of events in the fall-out from the escape of three dangerous prisoners from Parkhurst prison, it could provide the opposition with the evidence it needs to prove that the Home Secretary had been "less than frank" with the Commons.
The serving of the writ on Treasury lawyers yesterday co-incided with the release of a dossier from Mr Lewis which seeks to discredit the findings of the withering report into prison security by Sir John Learmont. Mr Lewis claims the Learmont report - which led to his summary dismissal as director-general of the Prison Service on Monday - contains numerous inaccuracies, is selective and could have been more "thorough and complete".
But the writ has the potential for far greater damage. Under the rules of disclosure, it gives Mr Lewis the opportunity to trawl through thousands of Home Office documents which support his allegation of wrongful political interference in the running of the service - a charge the Home Secretary has consistently denied. Critics say his denial enables him to distance himself from the service, and shrug off any blame of calls for his dismissal over for the current crisis in the Prison Service.
The writ claiming special damages for breach of his pounds 125,000-a-year rolling contract, states that Mr Lewis met all the key performance targets set for him by Mr Howard, but that any deficiencies in his performance - which he denies - were "substantially caused or contributed to" by the "high level" of wrongful involvement by the Home Secretary.
Of the removal of John Marriott, the Governor of Parkhurst prison - which is at the centre of the claims that Mr Howard misled the Commons - the writ alleges the Home Secretary placed "extreme and unjustified" pressure on Mr Lewis to suspend Mr Marriott. That pressure included a suggestion that Mr Howard would consider over-ruling Mr Lewis if he did not comply. Mr Lewis had intended to move him to a non-operational post.
It further alleges that, despite assurances given to the Commons, Mr Howard failed to act promptly to provide extra resources needed to carry out the security improvements recommended after last September's embarrassing escape by five IRA prisoners from Whitemoor prison.
In what will almost certainly further damage strained relations between the Home Office and prison officers, it also accuses the Home Secretary of requiring Mr Lewis to make "highly critical" public statements on actions by the Prison Officers' Association.
It also includes claims that Mr Howard delayed the recruitment of a personnel director for the service, pressurised Mr Lewis to increase the severity of internal disciplinary action, required him to delay restructuring area manager arrangements, and refused this summer to allow Mr Lewis to reduce the number of prisons holding Category A prisoners in order to improve security and reduce costs.
Those supporting the former television executive say that by the time the case comes to court there could well be other allegations arising out of disclosure. They include the controversial transfer of IRA prisoners and the supervision of high-profile prisoners like Rosemary West and Myra Hindley. It is alleged that Mr Howard ordered that their cell doors be kept open with an officer outside following the suicide of Fred West - an order overturned when governors pointed out they might escape.
Crucially it may reveal whether the Learmont report into Parkhurst has been "selective" with the evidence, as Mr Lewis claims.
Mr Lewis' letter to Mr Howard, which seeks to undermine the impact of the Learmont report, suggests that might be the case. The report omits a crucial piece of evidence from Sir Duncan Nichol - one of the Prison Board's non- executive directors - who described the inquiry's view of the Board's distance from the nuts and bolts of prison life as "a travesty of reality".
Mr Lewis claims it was he and his fellow Prisons Board members who were trying to re- focus efforts on to security after years in which both ministers and governors had taken their "eye off the ball".