The country’s highly decentralised system gives Spain’s 17 regions broad powers, meaning Vox’s entry into the regional government of Castilla y León, just north of Madrid, will give it a major impact on policy.

Vox said it would hold the second-highest position in the government of Castilla y León, where it came third in last month’s regional election.

Although the PP came first, it did not achieve an absolute majority, winning only 31 of the regional assembly’s 81 seats.

That left it vulnerable to pressure from Vox — which won 13 seats in a huge increase from the 2019 election where it secured just one.

“We have reached an agreement with Vox… that will allow us to establish a stable and solid government,” tweeted the region’s outgoing PP leader Alfonso Fernández Mañueco, who will be reinstated thanks to the deal.

Vox leader in the region Juan García-Gallardo will be Castilla y León vicepresident, the parties have agreed. 

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The ruling Socialist party immediately attacked the opposition PP over the deal, denouncing it as “a pact of shame”.

Founded in 2014, Vox started as a marginal force in Spanish politics before causing a major upset in late 2018 when it entered a regional parliament for the first time, winning seats in the assembly of Andalusia in the south.

Following national elections nearly a year later, it became the third-largest force in Spanish politics with 52 seats in the 350-seat parliament, mirroring gains elsewhere in Europe for the far right.

The regional governments of both Andalusia and the Madrid area are PP-led but supported from the outside by Vox in exchange for political concessions.

READ MORE: Why elections in little-known Castilla y León really matter for Spain’s future