The Australian investment firm Macquarie promised to invest £3 billion in green projects and made other concessions in order to clinch the purchase of the Green Investment Bank from the government.

However, the sale, in which the group will pay £2.3 billion, was criticised yesterday.

Nick Mabey, chief executive of E3G, a think tank that developed the idea of the bank, said that it was “reckless” because it would dampen investment in clean energy projects.

Ed Davey, the former Liberal Democrat energy secretary, said that it was “environmentally irresponsible”.

Macquarie was picked last year as the government’s preferred bidder for the bank, but it became bogged down in a row over whether it would asset strip the business. A rival bidder, Sustainable Development Capital, attempted to bring a judicial review of the auction but its challenge was rejected in the High Court two weeks ago.

Macquarie admitted yesterday that it would sell some of the bank’s early-stage investments. Yesterday it was announced that GCP Infrastructure, a FTSE 250 listed group, is investing in 23 Green Investment Bank projects that could lead to their acquisition.

Macquarie said that it would not rapidly divest substantial amounts of its assets. The bank will be retained inside Macquarie, becoming its European platform for investment in environmentally friendly technology, and its operations in London and Edinburgh will be retained.

The deal comprises a £1.7 billion price tag and £600 million in funding commitments for existing projects. The government has provided £1.5 billion since 2012.

Since its launch in 2012, the bank has committed £2 billion to projects including waste management plants and offshore wind farms. In 2015 the government decided to sell a majority stake to give the bank more freedom to borrow, release it from state aid restrictions and allow it to attract more capital.

Nick Hurd, the energy minister, said yesterday: “GIB will invest more into the green economy than ever before, with £3 billion of new investment targeted over the next three years, exceeding GIB’s track record of committing £3.4 billion of investment over the four and a half years since it was founded.”

To counter criticism that the bank would deviate from its mission under Macquarie’s ownership, the government has put in place a special share controlled by independent trustees, who will also oversee the bank’s green commitments. Any change to its articles of association would require consent from the trustees.

Macquarie is setting up three new funds drawing in investment from its consortium partners. One, a “green infrastructure investment platform”, will be supported by the government.

While proponents of the deal argue that it will boost opportunities for investment, critics believe that it will be counter-productive. Mr Mabey warned that with the European Investment Bank leaving because of Brexit, the UK risks losing two leading investors in clean energy.

Daniel Wong, head of Macquarie Capital, Europe, said: “The future for green investment is very positive globally and the Green Investment Bank, combined with the Macquarie platform, will be well positioned to source opportunities and deploy capital.”