The storm over Sir Fred Goodwin's pension has shown no sign of abating
Former RBS chairman Sir Tom McKillop has said there was no "elaborate ruse" to reward former chief executive Sir Fred Goodwin.
Sir Fred left "at the request of the company with his full contractual entitlement" because of the need for a "consensual departure", Sir Tom said.
"Each element of the proposed terms of departure" was discussed with City Minister Lord Myners, he added.
Sir Fred's £703,000 pension arrangement has sparked much public anger.
Sir Tom's comments were in a letter to the Treasury Select Committee.
Lord Myners earlier this month told the committee that he had known about Sir Fred's pension, but insisted he did not know about any discretion for the board in respect of paying that pension.
Lord Myners also said he had not "endorsed" Sir Fred's pension.
But a member of that committee, the Conservative MP Michael Fallon, said: "If he's misled parliament, and I think he has, then he should resign."
Lord Myners, Mr Fallon insisted, "told our committee he didn't get any information about the pension, he didn't ask for information, and he wasn't told about it".
"On the contrary, Tom McKillop makes it clear that Lord Myners was told each detail of the pension, the undiscounted effect - that's the mechanism by which it was doubled because he was taking early retirement - and the total."
The shadow chancellor, George Osborne, said Lord Myners must prove that his testimony to the select committee was true and resign if not.
Chancellor Alistair Darling said he would consider Sir Tom's letter and respond.
Sir Tom said in his letter that he and Bob Scott, the senior independent director, made a "full disclosure" of Sir Fred's compensation to Lord Myners.
"Mr Scott is certain that he discussed each element of the proposed terms of departure set out in the remuneration paper, including the pension," Sir Tom said.
"Mr Scott also gave Lord Myners... a range of £15m to £20m as being Mr Scott's best estimate of what the pension liability might be."
Lord Myners earlier this month told the Treasury Select Committee that he had not been privy to "the thinking of the remuneration committee or members of that committee of RBS".
In his letter, Sir Tom said: "I must emphasise that there was no 'elaborate ruse' by myself and Mr Scott to give Sir Fred any more than he was contractually entitled to and that we and, I believe, all the directors acted in what we judged to be the best interests of the shareholders, including the government."
Sir Fred took early retirement from RBS last year after the bank needed a £20bn bailout from the government. The payout has been widely condemned.
Sir Fred's Edinburgh home was attacked by vandals last week.
UK Financial Investments, which manages the government's stake in RBS, said it would register a protest vote against Sir Fred's pension at the bank's annual meeting on Friday.