The bus company Arriva has apologised for “inappropriate” behaviour after an on-duty driver offered express support to anti-Israel protesters.

The incident in November, outside Sadler’s Wells theatre in London, was during a demonstration against a performance by the youth arm of Israeli dance company Batsheva.

Activists were gathered outside the venue wielding banners about Israeli apartheid at the demonstration, when the driver of a No 38 bus came past. As he passed, the driver tooted his horn several times and waved at the demonstrators, promoting them to cheer.

A witness contacted Arriva the following day expressing concern, and Arriva has now investigated.

“That sort of behaviour is totally inappropriate whilst on duty and I can confirm that the driver in question has since been identified and interviewed by his manager,” said a spokesman for the company “He was advised on all aspects of your complaint and his performance will be closely monitored to make sure that there are no further incidents of this nature.

“I am sorry that a member of our staff should have acted in this manner.”

A Transport for London spokesman, responding to another complaint about the incident, said: “We expect drivers to promote a positive image of London Buses and to act professionally at all times. Clearly, a London bus driver should not be participating in a protest while performing their duties.”