The Wellcome Trust’s director has defended the charity’s investments in fossil fuel firms, arguing that it uses its position as a shareholder to influence companies.

Earlier this month The Guardian launched a campaign urging the Wellcome Trust and the Bill and Melinda Gates Foundation to divest from fossil fuel companies. So far more than 145,000 people have signed the petition.

In a comment piece published in The Guardian last week, Wellcome Trust director Jeremy Farrar said: “The Trust has significant common ground with The Guardian’s fossil fuel campaign.”

He said that the Trust has spent £32m since 2010 on research addressing the impact a warmer world has on health.

“We do not agree, however, that the strongest contribution the Trust can make to a decarbonised economy is a commitment to avoid investing in a list of 200 fossil-fuel companies, compiled according to the size of their reserves rather than the position they take on climate issues,” he argued.

He added that the charity invests on a “case-by-case” basis and that by actively engaging as shareholders it is able to positively influence companies.

“We understand the attraction of the grand gesture for which The Guardian is calling, but such a gesture can be made only once. By maintaining our positions, we meet boards again and again, supporting their best environmental initiatives and challenging their worst.

“We would not be able to have the frank discussions we require if we published details, but we are confident that our engagement has impact. Were we to sell our holdings, it is unlikely that the buyers would exert the same influence. But when we are not satisfied that a company is engaging with our concerns, we are perfectly prepared to sell,” he said.

• In the March issue of Charity Finance Danny Truell described the Wellcome Trust’s investment strategy, online subscribers can read it here. Find out more about subscribing to the magazine here.