Anyone watching the Labour leadership’s refusal to rule out a post-election agreement with the SNP, would be forgiven for thinking such an arrangement was unique. However, explains Daniel Cetrà, pro-independence parties offering support to minority governments is nothing new – as evidenced by Spain.

There has been a great deal of comment recently about the prospect of the SNP supporting a minority Labour government in Westminster.

Parts of the press present this scenario as terrifying, and the Tories have added to that for electoral reasons. ”You could end up with an alliance between the people who want to bankrupt Britain and the people who want to break up Britain”, warns David Cameron. That this would almost certainly be a confidence-and-supply agreement, rather than an outright coalition, is not seen as especially significant.

But would this scenario be in any way unique? Is there any experience in continental Europe of pro-independence parties supporting minority governments at the centre?

Spain provides an interesting case in point. In the period 2004 - 2008, there was a confidence-and-supply agreement between a minority Socialist government and the Catalan pro-independence and centre-left ERC (Esquerra Republicana de Catalunya). It was a multi-level coalition: ERC and the Catalan Socialist party (PSC), a sister party of the Spanish socialists, were at the time in the Catalan coalition government, together with the Catalan Greens.

The Socialist Party (PSOE) won the 2004 Spanish general election, obtaining 164 seats but falling 12 short of majority. In the same vote the ERC, which previously had only a single deputy in the Spanish Parliament grew significantly, winning eight seats. The Socialist Party needed the support of two smaller parties, and the ERC saw this situation as an opportunity to achieve one of its fundamental goals: the reform of the Catalan Statute of Autonomy.

The Socialist Party was able to secure a working parliamentary majority between 2004 and 2008 by reaching deals with both ERC and the leftist coalition United Left.

The two parties prioritised their ideological proximity over their constitutional differences and agreed on a number of social policies. ERC provided parliamentary support to pass the 2005 and 2006 Spanish budgets, while the National Hydrological Plan, strongly opposed by ERC, was abolished.

But the revision of the Catalan Statute caused severe tensions. Essentially, the Catalan government wanted a new Statute in order to obtain further political powers and economic resources, as well as national recognition for Catalonia, which was symbolic but would also imply bilateral relations with the centre in some areas. Dependent on the parliamentary support of ERC, the Socialist government of José Luís Rodríguez Zapatero was not in a position to dismiss demands for further autonomy.

However, the Socialist party declared its intention to amend substantial articles of the draft passed by the Catalan parliament. Negotiations extended during a period of intense discussions in the media and in the face of strong opposition from the right of centre People’s Party (PP). Unexpectedly, in January 2006 the then Catalan opposition leader Artur Mas (CiU) reached a global agreement with Zapatero, bypassing the then Catalan government. ERC believed the original content was excessively diluted, and also felt undermined by this agreement, since CiU and ERC compete for the leadership of Catalan nationalism. ERC ended up rejecting the modified version approved by the Spanish parliament.

This process caused a rift between the Socialist party and ERC. The mistrust extended to other policy areas, with ERC voting against important laws such as the 2007 Spanish budget and the Law of Historic Memory. The ERC also withdrew from the Catalan coalition government as a result of tensions with the PSC following the Statute revision process, although it joined again in 2006.

In conclusion, the confidence-and-supply agreement in Spain did not result in easy constitutional change. Disagreements between PSOE and ERC were the norm until Mas bypassed ERC and reached a deal with Zapatero, and during the process the PP radicalised its opposition to any form of constitutional change.