India's top court has granted businessman Subrata Roy, negotiating the sale of his assets, including hotels in London and New York, from a makeshift office in prison, a 15-day extension to seal a deal, media reports said.

Roy, who heads troubled financial services group Sahara India Pariwar, was initially allowed 10 working days to 19 August to talk to bidders eyeing his assets, including the Grosvenor House in London.

The Supreme Court also said that the extension will be Roy's last.

A deal will help Roy raise funds to post a $1.65bn (£989m, €1.2bn) bail in Delhi. Roy has to pay India's market regulator Sebi to get out of Tihar jail.

Roy's steno, secretarial assistants and Sahara directors Ashok Roy Choudhary and Ravi Shankar Dubey were given access to a conference room in the prison earlier in the month, following a court order.

American real estate investor Madison Capital has tabled an $800m bid for Roy's US hotels – the Plaza Hotel and Dreams Downtown Hotel.

The Sultan of Brunei, an investment arm of the Qatari royal family and Indian pharma billionaire Cyrus Poonawalla have all offered to buy the British property, which is located in the Mayfair area and managed by J W Marriott.

Roy has been in jail since 4 March after two group companies - Sahara Housing and Sahara Real Estate - failed to comply with the Supreme Court's order to refund $3.9bn to 30 million investors.

Roy acquired the New York hotels for close to $800m in 2012 and had purchased the Grosvenor for $725m in 2010. The acquisitions were financed through borrowings from the Bank of China.