Johann Lamont has resigned as leader of the Scottish Labour Party accusing the Westminster leadership of treating the party in Scotland as a "branch office".
Relatives and friends of people who died while in police custody have marched to Downing Street to demand justice for their loved ones.
The United Families and Friends group, which organised the event, said about 300 protesters took part in the annual procession, which started in Trafalgar Square and marched down Whitehall.
Activists carried placards which read "No Justice No Peace" and banners in memory of those such as musician Sean Rigg, who died after being restrained at Brixton police station, south London, in August 2008.
Deborah Coles, director for the Inquest campaign group, said the procession was an "important but poignant" day for the families.
She added: "Many families feel betrayed by a system that has let them down.The same issues repeat themselves time and again despite the empty platitudes from Government ministers that lessons will be learned."
US Central Command says America and its allies conducted 22 air strikes against Islamic State in Iraq on Friday and Saturday.
The outgoing chair of the Scottish Labour Party said "it has been an immense privilege to lead" the part during the "momentous time in Scottish politics."
In her resignation letter, Johann Lamont said she believed Labour Party is the "only chance for better Scotland."
"Despite the serious challenges we face, I strongly believe that the Labour Party is not only our best chance of achieving a better, fairer Scotland, it's our only chance," she said.