Sky News has learnt that Edi Truell, a City financier who lodged a bid last year for Tata Steel's UK operations, including the Port Talbot steelworks, has written to the trustees to outline a revamped offer aimed at rescuing the £15bn scheme.
It refers to an audacious plan to merge Tata Steel's speciality unit with Sheffield Forgemasters, an advanced steel materials business which has been struggling to address doubts about its financial future.
Mr Truell's charity would then provide £200m of additional investment into the combined group, while taking on responsibility for the Tata Steel UK pension liabilities.
According to the letter, a copy of which has been obtained by Sky News from sources in Whitehall, Mr Truell has requested that he and Luke Webster, a public sector pensions executive, be "co-opted as trustees, and so be inside the tent...to find a solution".
He also questioned trustees' assertion in a newspaper interview last week that the UK steel operation "was close to insolvency".
"If the business is now 'close to insolvency' despite being profitable, then how could the directors of Tata Steel UK have been continuing to trade earlier in the year?", Mr Truell wrote.
Allan Johnston, the chair of the trustees, told the Financial Times last week that they were "in meaningful negotiations" with Tata Steel about an injection of several hundred million pounds into the 130,000 member-strong scheme.
Such a structure would be intended to release the security held by the pension fund over a Dutch Tata Steel plant, paving the way for a merger between the Indian-owned company and Germany's Thyssen-Krupp.
Tata Steel has vowed to keep the Port Talbot plant in south Wales open for at least five years if it is able to detach the retirement scheme.
Some pension experts - including Mr Truell and John Ralfe, a leading industry consultant - have questioned the viability of the plan, however, because it will leave the steelworkers' scheme without a sponsor.
The Pensions Regulator said last week that there were "still significant issues to be resolved" before approval could be given to separate the British Steel Pension Scheme from the sponsoring company.
Mr Truell's plan faces the added complication that Tata Steel is already negotiating over a sale of its speciality unit to Liberty House, although his letter suggests that the seller's advisers had reached out again to other potential buyers.