Over 200 writers have threatened to boycott literary festivals across the UK unless the investment firm which sponsors them divests from Israel and fossil fuels.

Authors including novelist Sally Rooney, social campaigner Naomi Klein, journalist George Monbiot and writer Robert Macfarlane, have signed a statement by Fossil Free Books (FFB) which demands asset management firm Baillie Gifford withdraws all investment from Israel.

The group is calling on Baillie Gifford to divest “from companies that profit from Israeli apartheid, occupation and genocide”, and says it believes that “solidarity with Palestine and climate justice are inextricably linked”.

Baillie Gifford sponsors the UK’s most prestigious nonfiction accolade, the Baillie Gifford Prize for Nonfiction, as well as the Hay Festival, Cheltenham Literature Festival and Edinburgh International Book Festival.

The writers say that literary organisations that accept sponsorship from Baillie Gifford “can expect escalation, including the expansion of boycotts, increased author withdrawal of labour, and increased disruption until Baillie Gifford divests”.

The letter says that Baillie Gifford has “Nearly £10 billion invested in companies with direct or indirect links to Israel’s defence, tech and cyber-security industries.”

It added, “A literary industry free from fossil fuels, genocide and colonial violence is possible and it is necessary.”

“Until the firm agrees to divest, we call on all literary organisations, including festivals, to end their relationships with Baillie Gifford.”

The investment company came under fire last year at the Edinburgh International Book Festival by writers including Zadie Smith, Ali Smith and Katherine Rundell. Greta Thunberg withdrew from her appearance at festival.

Last year, Nick Thomas, a senior partner at the firm, said Baillie Gifford was been surprised by the criticism as only 2 per cent of its funds were in the fossil fuel industry, compared with 11 per cent for the asset management sector as a whole.

A spokesperson for Baillie Gifford told the Guardian this week that divesting in the way that FFB asks is not possible because of UK asset management regulations.

“We are managers of other people’s money, not our own”, they said. “We are not in a position to make exclusions of that nature based on our own ethical judgements, or in response to pressure from outside groups.”

Baillie Gifford said FFB’s assertion that the company has “nearly £10bn invested in companies with direct or indirect links to Israel’s defence, tech and cybersecurity industries” is “seriously misleading”.

The spokesperson said that while the company’s clients have invested in multinational technology companies including Meta and Amazon which have dealings with Israel, these are “tiny in the context of their overall business”.

The spokesperson added that “practically every consumer and investor in the developed world is using the services of these companies.”

FFB was formed soon after the furore at the Edinburgh festival.

The group was behind a controversial motion put forward to the Society of Authors (SoA) earlier this month, which called for the SoA to say it supported an immediate ceasefire in Gaza and condemned Israel’s “targeting” of writers. The literary union voted down the motion.

Another FFB proposal, which called for the book industry to divest from Baillie Gifford, was approved by the SoA.