Almost 250 senior academics based in the UK have penned an open letter condemning legal threats against universities during Israel Apartheid Week, saying criticism of Israel is not the same as anti-Semitism.

The letter, published in The Guardian on Monday and signed by 244 professors, lecturers and researchers, says the new working definition of anti-Semitism adopted by Theresa May in December effectively outlaws free speech on Israel.

The group slams Universities Minister Jo Johnson for urging Universities UK to adopt the new International Holocaust Remembrance Alliance definition, which expands on previous guides and now includes reference to Israel being racist.

The academics also lambast grassroots group Campaign Against Antisemitism for encouraging supporters to film events on campus with a view to pressing charges.

“These are outrageous interferences with free expression, and are direct attacks on academic freedom,” they write. “We express dismay at this attempt to silence campus discussion about Israel, including its violation of the rights of Palestinians.”

They add: “It is with disbelief that we witness explicit political interference in university affairs in the interests of Israel under the thin disguise of concern about anti-Semitism.”

Among the signatories are peers of the realm and heads of department at some of the country’s most prestigious universities, some of whom are Jewish.

It comes after the University of Central Lancashire last week cancelled an Israel Apartheid Week event featuring journalist Ben White after letters sent by pro-Israel lawyers and peers warning against legal challenges. The academics, in their open letter, said this decision was made “in haste and clearly without legal advice”.