Leading academics have been accused of undermining a protest about workers’ rights in London in order to give a talk about a historian famous for his support of workers’ rights.

Sir Richard Evans was due to discuss his book on Marxist historian Eric Hobsbawm at the University of London on Thursday evening, breaking a boycott supported by hundreds advocating better employment conditions for cleaners and other outsourced staff at the university.

Martin Jacques, the former editor of Marxism Today, and Prof Donald Sassoon, who completed his PhD under Hobsbawm’s supervision, were also scheduled to talk.

“It is disappointing that these respected academics chose to ignore the boycott in order to talk about a Marxist historian that we are sure would be on our side in this struggle,” said Maritza Castillo Calle, University of London branch chairwoman of the IWGB union, which has organised the boycott.

Evans, regius professor emeritus of history at Cambridge University, said he supported the cause of the protesters and would “bring it to the attention of the meeting”. The other scheduled speakers did not respond to the Guardian’s requests for comment.

The talk has been organised by the Institute of Historical Research at Senate House, where it is being held, and Birkbeck University history department, despite the university’s student union supporting the boycott.

A statement from Birkbeck University said the institution was “strongly supportive of the University of London’s decision to bring currently outsourced staff into direct employment of the university – a process which is currently under way”.

An IWGB spokesman disputed the matter, however, saying: “The bulk of outsourced workers – including maintenance, cleaners and catering – will remain outsourced at least until their contracts are up for tender in 2019, 2020 and 2021. At that point, an in-house bid will be presented alongside other commercial bids, leaving the door open for the workers to remain outsourced indefinitely.”

The union, which has also campaigned on behalf of Uber drivers, has been fighting to have the workers taken in-house since September 2017, and escalated its efforts in December last year, when it took the step of leading a boycott. The IWGB said its action focused solely on University of London central administration, not the constituent colleges, such as UCL and SOAS, which have a different management.

It is understood several supporters of the boycott planned to attend Thursday’s event.

Evans said: “I think it is right that outsourced labour should be brought under the aegis of the University of London and given the same working terms and conditions as those employed by the university directly. I understand the university is making efforts to do this.”

More than 400 academics and politicians, including the shadow chancellor, John McDonnell, as well as academic institutions and other leading figures, are backing the boycott over the University of London’s “continued use of outsourced workers to provide essential services”.

Staff paid by outsourced companies are demanding equal terms of employment with those employed directly by the university.

Castillo Calle said the boycott was “a last resort following countless strikes”. She added: “We hope the stand taken by our supporters will make university management finally see sense.”

• Letter from Richard J Evans: ‘Eric Hobsbawm would not have backed University of London boycott’