Businessman Adar Poonawalla, whose family bid for the Lincoln House in south Mumbai for Rs 750 crore, has blamed “bureaucratic harassment” for being unable to take possession of the heritage mansion.

The billionaire Poonawalla family, which runs the Pune-based vaccine manufacturer Serum Institute of India, bid for the property in 2015 with an offer of Rs 750 crore, making it the most expensive residential property deal in the country.

Four years later, after paying a “substantial” amount, the family is yet to get the property’s possession, Adar Poonawalla, the chief executive of the Serum Institute of India, said.

He blamed “bureaucratic harassment” by officials for the troubles. The two-acre property, once owned by the erstwhile Maharaja of Wankaner, stands on land owned by the defence establishment, and was taken by the US government to house its consulate since 1957. The consulate later moved to the Bandra-Kurla Complex business district.

The Poonawalla family had struck the deal with the US, which involved transfer of the lease rights.

“I’d have never touched the property if I feared it will get into a trouble. The lease is for 999 years and began in 1957. We have 900 more years,” Poonawalla said.

Poonawalla said he did not receive any specific reasons for the deal delay. Over the past four years, he has met bureaucrats in the defence ministry and also then defence ministers Arun Jaitley and Manohar Parrikar for expediting clearances. Poonawalla said the issue was now with the Prime Minister’s Office as it involved two sovereigns.

Nick Novak, spokesperson for the US Consulate in Mumbai, said: “The US government is seeking to work with the Indian government on the transfer of the Lincoln House lease in accordance with the terms of the lease. We expect to be able to complete the transfer in the near future.”