Sir Philip Green's offer to contribute to the BHS pension scheme was £100m less than the Pensions Regulator wanted, according to reports.
The BBC has said that the regulator wants £350m from Green, but he was only willing to put in £250m.
Yesterday, the regulator announced that it was starting legal action against Green to seek financial aide for the 20,000 BHS pensioners. Negotiations between the two parties have been going on for four and a half months.
Green said in a statement yesterday that he had made a "credible and substantial proposal" to the Pensions Regulator, "with evidence and bank confirmation of cash availability".
But the offer was not enough, and now the regulator will have to go through the legal route to get money from Green.
Lesley Titcomb, chief executive of the Pensions Regulator (TPR), said: “Our decision to launch enforcement action is an important milestone in our work to attain redress for the thousands of members of BHS schemes who have been placed in this position through no fault of their own.”
Frank Field MP, chair of the Work and Pensions Committee, said he was "not surprised" that the regulator had "lost patience" with Green.
"His answer throughout our inquiry was always that he was going to ‘sort’ the disastrous position he left the pension fund in when he sold off BHS to Dominic Chappell for £1," Field said.
"We are glad to see TPR is now calling his bluff and instigating enforcement proceedings. It seems clear Sir Philip would rather kick the can down the road and avoid responsibility than come up with any fair, sustainable settlement for BHS pensioners."
Philip Green has been approached for comment.