The BBC has defended its Panorama programme on the Gaza flotilla incident amid a barrage of complaints from pro-Palestinian supporters.

Led by the Palestine Solidarity Campaign, demonstrators protested at BBC offices in London, Manchester and Bristol on Sunday against "shockingly biased reporting".

In Death in the Med, presenter Jane Corbin interviewed IDF soldiers and activists involved in May's incident. She concluded that those on board the Mavi Marmara had been politically motivated and had not acted primarily to help Palestinians.

At BBC Television Centre, demonstrators' chants included: "BBC, shame on you. In our thousands, in our millions, we are all Palestinians." But only around 25 people attended the protest.

Among those present were supporters of the Islamic IHH organisation, which is accused of having links to terrorist groups, and activist Ken O'Keefe, who took part in the Panorama programme and was on the Mavi Marmara.

He told Iranian-backed Press TV: "We need to realise the BBC is a propaganda tool. In a way I consider this programme as a gift because it helps expose the BBC's support for an unjustified war. Now more of us can go to real news sources, to real journalists, to get information."

The BBC offered a robust defence. In a statement Panorama bosses said: "Jane Corbin is a world-renowned journalist with 20 years' experience reporting for Panorama on the on-going conflict in the Middle East. She is respected for her dedicated, impartial and balanced work from both sides of the conflict ."

During the protest, the Zionist Federation's Jonathan Hoffman hand-delivered a letter of support to the corporation.

It stated: "Death in the Med was, for the most part, balanced, well-researched and well-documented. We deplore the personal attacks on Jane Corbin which include the accusation that she is somehow in the pay of the Zionist lobby."

The National Union of Journalists also defended itself against allegations that it had encouraged members to complain to the BBC.

Rod Alexander, NUJ head of campaigns, said: "We have not instructed members at any stage to complain to the BBC." It is thought NUJ vice-president Donnacha DeLong, previously an editor on Amnesty International's website, had acted in a personal capacity when he emailed members asking them to attend the protests and encouraging BBC staff to go on strike.