Infrastructure investor Macquarie has written to UK ministers to confirm it has financed billions of pounds of environmentally friendly projects as part of an agreement in its purchase of the Green Investment Group from the government three years ago.

The Australian company promised to finance £3bn in green energy projects in the UK and Europe over the three years following its £1.6bn acquisition of the group, which was then known as the Green Investment Bank, in August 2017.

Macquarie said that, by October 2020, the group had agreed £4.7bn in financing in the UK and Europe, and £6.9bn worldwide. About £3.1bn of this financing is in the UK.

In a letter to Kwasi Kwarteng, the UK minister for energy, Daniel Wong, global co-head of Macquarie Capital and chair of the Green Investment Group, said it had “remained true to its original mission”.

The letter added that its growth reflected the “objectives of the UK government, in allowing GIG the freedom to increase the sectors and technologies in which it operates, commit ever greater levels of capital to green projects, and expand its operations internationally to export this UK success story overseas”.

The bank was set up under the coalition government in 2012 to draw private capital into offshore wind farms, waste-to-energy plants and energy-saving projects.

It launched a sale process three and a half years later to reduce public debt. The government had also concluded there was enough private capital in the market and a risk that the bank was adding to competition in the sector, according to a National Audit Office report on the sale.

By the time it was sold in 2017, the bank had invested in 100 projects with a total transaction value of £12bn, committing £3.4bn of its own capital.

However, the NAO concluded that not enough information was available “to assert the degree to which the GIG was the cause of the growth in the green economy since 2012”.

More than half the investment capital went to wind farms, where the UK is now the global leader in offshore capacity, according to a recent Global Wind Council Work Energy Report.

The sale of the bank was widely criticised at the time by MPs including Vince Cable, Liberal Democrat leader at the time, who questioned Macquarie’s commitment to environmental projects.

But Mark Dooley, global head of the Green Investment Group, said that the GIG “had done its job” by the time of the sale. The UK remains one of the most “investable energy and infrastructure markets in the world”, he said.

He added that since taking over the bank Macquarie had “more than delivered — triggering private capital markets to support renewable energy markets”.

It is now in 25 countries and employs 450 staff, including 40 in Edinburgh. It is increasingly looking to invest earlier in the development and construction process, including in renewable energy storage.

Mr Dooley pointed to an upsurge in corporate clients. These include Tesco, which is working with the GIG to install solar energy at a number of properties in the UK, and Amazon, which has recently announced plans to invest in 127 solar and wind projects, making it one of the world’s largest corporate buyers of green energy.

He said government plans to create another UK infrastructure bank, expected to be much like the GIG, could work if it invested in the earliest-stage technologies that are struggling to get finance. The government has pledged to announce more details in the spring.