Macquarie Group Ltd. will likely receive approval from the U.K. government to buy UK Green Investment Bank Plc in January 2017, The Australian Financial Review reported, citing "a person familiar with the process."

The sale of the bank is expected to complete before the end of March 2017, in line with a deadline the government set when it announced the privatization earlier this year, the person added.

The investment bank could be valued at as much as £4.2 billion, including investments that the new owners will be expected to make in the next three years, said the British bank's CEO, Shaun Kingsbury.

Both UK Green Investment Bank and Macquarie declined to comment on the matter, the publication added.

Meanwhile, U.K. lawmakers, as well as Gregory Barker, a former climate change minister, have raised concerns that a new owner may lose the bank's environmental mission following the sale, even though five special shareholders with veto power have been appointed.