Jeremy Corbyn and Vince Cable have both condemned police violence in Barcelona after voters there were prevented from participating in the Catalonia independence referendum.
More than 460 people were injured as scenes turned ugly when police stepped in to stop what the Spanish government said was an illegal vote.
Around a dozen police officers were injured. Barcelona's mayor Ada Colau slammed police action against the "defenceless" population as they closed almost 100 polling stations in the region.
Spain's deputy prime minister Soraya Saenz de Santamaria defended police, saying they acted in a proportionate way – but UK politicians have disagreed.
Corbyn said the scenes were "shocking" and appealed for prime minister Theresa May to act:
Liberal Democrat leader Vince Cable said the police response had been "brutal and disproportionate" and told the foreign secretary to call upon the Spanish ambassador to tell him it was unacceptable.
"Police in a democracy should never drag people violently out of polling stations, whatever the arguments for or against holding a referendum," Cable said.
"The police response looks to have been brutal and completely disproportionate. The foreign secretary should break off from conspiring against the prime minister and call in the Spanish ambassador to tell him that this is completely unacceptable."
The referendum was being closely watched in Scotland and first minister Nicola Sturgeon added her concerns.
"Some of the scenes in #Catalonia this morning are quite shocking and surely unnecessary. Just let people vote," she tweeted.
She added: "Regardless of views on independence, we should all condemn the scenes being witnessed and call on Spain to change course before someone is seriously hurt. Let people vote peacefully."