Roland Rudd, one of the leading campaigners in the fight to keep Britain tied closely to the EU, has stepped down as a director of the company behind the People’s Vote group.

In a move one insider said marked as a “sorry end” to the slow decline of the movement forged during the fierce battle over Brexit, Rudd and another director, Richard Reed, resigned and handed over the reins of PV Campaign Ltd to Mark Kieran.

Kieran, a former civil servant, will be tasked with transforming the business into a wider campaigning organisation no longer devoted solely to the EU cause; instead it will focus on driving voter registration, pushing for electoral reform and standing up against racism. Allies praised him as “intelligent, bright and liberal”.

Rudd, 60, who last year was appointed chair of the Tate, is said to still favour closer alignment between the UK and EU but also says the referendum battle is over and that he wants to move on from the campaign group to let it flourish with new, younger blood. He declined to comment when approached by the Guardian.

The resignation signalled a significant moment for the group which, along with a host of celebrity backers, supported a second referendum. People’s Vote felt a rerun of the 2016 vote was in their grasp when exasperation over the Brexit stalemate reached its height in 2019.

Rudd, whose sister Amber Rudd is a former Tory home secretary, had stepped back from the organisation during the later part of that year after unsuccessfully trying to strengthen his grip on it – prompting a fiercer-than-expected backlash from the component campaign groups.

But now, more than five years after Brexit, Rudd and Reed have resigned from both PV Campaign Ltd and Open Britain Limited (formerly known as The In Campaign Ltd).

Open Britain was one of the campaigns that came together under the People’s Vote umbrella, which included Our Future Our Choice, Britain for Europe and For Our Futures’ Sake.

A former People’s Vote staffer said that while Rudd might have moved on, many of the staff whose lives and livelihoods were “destroyed” when the campaign fell apart in late 2019 had found it harder to do so. “This is a sorry end to a promising campaign which held the government to account for a shoddy Brexit deal.”

The Labour peer Andrew Adonis said the pro-EU flame continued to burn through the work of the European Movement group he chaired, and that it had a record number of members and more than 100 local groups that were “growing steadily”.