LONDON (Reuters) - The British government said it will sell the Green Investment Bank (GIB) to a consortium led by Macquarie Bank (>> Macquarie Group Ltd) in a deal worth 2.3 billion pounds ($3 billion), which critics said failed to guarantee its future.

The Australian bank's purchase of GIB, which backs green projects with public funds, had been expected since a court rejected the claim of a rival bidder earlier this month, but it has been vehemently opposed by environmental groups and some UK lawmakers.

They say Macquarie will strip the bank of its assets, potentially diluting its purpose of investing in green projects.

The government set up GIB in 2012 as a commercial venture to spur private investment in green projects. It has invested more than 2 billion pounds in projects such as offshore wind farms and waste management.

The deal comprises a 1.7 billion pound price tag and approximately 600 million pounds in funding commitments for existing GIB projects.

The government has provided 1.5 billion pounds since 2012, meaning that the transaction price at the date of signing represents a 160 million pound premium on total government funding.

The government decided to sell a majority stake in 2015, saying that would give the bank more freedom to borrow, free it from state aid restrictions and allow it to attract more capital.

"ENVIRONMENTALLY TOXIC"

The consortium's structure - comprising Macquarie Group, Macquarie European Infrastructure Fund 5 and Universities Superannuation Scheme - includes a "special share" arrangement whereby GIB's mandate would be safeguarded by five independent trustees, Macquarie said.

Macquarie pledged on Thursday to invest 3 billion pounds in green energy projects over the next three years. There were no guarantees on GIB's headcount as part of the deal but Macquarie said it would continue to operate from offices in London and Edinburgh, managing more than 4 billion pounds of green infrastructure assets and projects.

Critics said the government had failed to guarantee the future for the GIB's green credentials and criticised it for a lack of transparency.

"Selling the Green Investment Bank is environmentally irresponsible, and on the eve of an election is politically dubious. The government clearly hopes to avoid parliamentary scrutiny," said Ed Davey, former Liberal Democrat Secretary of State for Energy and Climate Change, referring to a national election in Britain to be held on June 8.

Bankers close to the deal, who did not want to be named, said there was little an investor could do with the bank except sell its assets.

"The GIB loses money, with two offices it is hugely expensive and there are no synergies between the businesses it runs," said one.

Daniel Wong, head of Macquarie Capital, Europe, said the bank would stand by its commitments.

"We understand the responsibilities that come with this ownership, and we are fully committed to maintaining its green purpose as we grow the business," Wong said.

A spokeswoman for Britain's Department for Business, Energy & Industrial Strategy said Bank Of America Merrill Lynch [BAC.N] advised on the sale but declined to disclose its fee.

(Editing by Nina Chestney and Susan Fenton)

By Oleg Vukmanovic and Dasha Afanasieva

Stocks treated in this article : Bank of America Corp, Macquarie Group Ltd