Image copyright National Trust Images/John Millar/PA Wire

The National Trust has announced that it will sell off the shares it holds in fossil fuel companies.

At present, 4% of its £1bn stock market investment is in such firms.

The Trust, the biggest conservation charity in Europe, said it wanted to invest in green start-ups and portfolios that benefited nature and the environment.

It said it had set a three-year timescale for the change, but most shares would be sold within a year.

Until now, the Trust had been prepared to invest in firms that derived less than 10% of their turnover from the extraction of thermal coal or the production of oil from tar sands.

That same threshold was also adopted by the Church of England in 2015. A year ago, however, the Church's General Synod voted to withdraw investment from companies that do not meet the terms of the Paris climate agreement by 2023.

And last month, the Norwegian parliament approved plans for the country's sovereign wealth fund, which manages $1tn (£786bn) of the country's assets, to sell coal and oil investments worth $13bn and invest in renewable energy projects instead.

"Over the years, we've gradually evolved our investment strategy to reduce our carbon footprint," said the Trust's chief financial officer, Peter Vermeulen.

Speaking to the BBC's Today programme, he added: "As a conservation charity [we] believe that after decades' worth of lobbying not enough has been done by the oil and gas companies, and for that reason we're looking to withdraw our investment and invest in companies that are looking to deliver environmental benefits as well as financial returns."

He acknowledged that oil giants such as BP and Shell were investing in renewable energy, but said that while their investments were "not insignificant", they were "too small as a proportion of their total capital investment".

"Still less than 10% of the oil major's investment is on low-carbon technologies and we believe that's not sufficient," he said.

The Trust said it analysed the carbon footprint of its investment portfolio every six months.

It said it also required all its investment managers to be signatories of the United Nations Principles for Responsible Investment.

The National Trust is responsible for the upkeep of 248,000 hectares of land, 780 miles of coastline and more than 500 historic buildings and parks across England, Wales and Northern Ireland.

It has 5.2 million members and more than 60,000 volunteers.