GUARDIAN and Observer journalists began a 48-hour strike today over the planned sale of the world’s oldest Sunday newspaper to loss-making start-up Tortoise Media.

Members of the National Union of Journalists (NUJ) rallied outside the titles’ headquarters in London, their first walkout for more than 50 years.

Among those joining the crowds of staff were artist Grayson Perry, TV presenter Anne Robinson, authors Lemn Sissay and Michael Rosen, comedian Stewart Lee, TUC general secretary Paul Nowak, RMT general secretary Mick Lynch, independent MPs John McDonnell and Rebecca Long Bailey, and Labour MPs Andrew Pakes and Steve Witherden.

“It’s a fantastic turnout,” said NUJ general secretary-elect Laura Davison from the picket line.

“Many are here showing solidarity and saying it’s too important for a deal to be done behind closed doors and too important for wider public life.

“People are calling on management to meaningfully engage with staff, who are the people who create the success of the titles, and saying there needs to be proper scrutiny and an opportunity to look at alternatives.

“The Observer holds a unique and important place in public life and our members care about the next chapter in its history.

“The union is calling for a pause in the exclusive talks to provide more time to consider alternatives and ensure decisions are in the best interests of both titles.”

The strike coincides with the Observer marking 233 years since first publication.

A Guardian spokesperson said: “We recognise the strength of feeling about the proposed sale of the Observer and appreciate that NUJ members wish to make their views heard.

“While we respect the right to strike, we do not believe a strike is the best course of action in this case and our talks with the NUJ continue.”