Hundreds of thousands of people protested in Madrid on Saturday against an amnesty law agreed by Spain's Socialists over Catalonia's separatist bid back in 2017, in order to form a government.

This latest demonstration happened just two days after the country's Socialist Prime Minister Pedro Sanchez secured a four-year term with the support of Catalan and Basque nationalist parties in return for agreeing to the amnesty law, Reuters reports.

Around 170,000 people took to the streets of Madrid, waving Spanish flags and signs stating "Sanchez traitor" and "Don't sell Spain." According to opposition parties, judicial associations and business leaders, the amnesty law jeopardises the rule of law and the separation of powers.

Attending the protests organised by civil groups were the opposition conservative People's Party leader, Alberto Nunez Feijoo and leader of the far-right Vox party, Santiago Abascal.

The amnesty will cover hundreds of Catalan separatists in legal difficulty after the illegal 2017 secession bid that led to the country's largest crisis in decades, El País reports.

It will be Spain's largest since the blanket amnesty in 1977 for crimes committed during Franco's dictatorship.

Sanchez spoke in defence of the law, saying an amnesty would help to ease tensions in Catalonia. He won a parliamentary vote to form a new government last Thursday by 179 votes for and 171 against, the Reuters report adds.

Since the agreement was announced, protesters held demonstrations outside the Socialist headquarters in Madrid for 15 straight nights, with some clashes with police leaving protesters and officers injured.

A survey carried out back in September by Metroscopia showed around 70% of respondents – 59% of whom were Socialist supporters – were against an amnesty.