One of the most curious stories in the last few weeks has been the news that Pedro Sánchez is not resigning. Spain's Socialist prime minister, had threatened to quit after anti-corruption campaigners brought charges against his wife, Begoña Gómez. The Madrid prosecutor, meanwhile, has asked the court to dismiss the charges against Gómez. After keeping everyone in suspense for a long weekend, Sánchez decided to stay.

What superficially may appear like grand political theatre, reflects one of the most toxic political cultures in western Europe. The same happened to the conservative opposition too. The husband of Isabel Díaz Ayuso, president of the regional council of Madrid, is under investigation by Spanish tax authorities. In Spain law and politics intermingle more than in other countries.

Nowhere does it intermingle more than in the politics of Catalan independence. After last year's general elections, Sánchez is governing with the help of regionalist parties from Catalonia and the Basque region. One of them is Together for Catalonia, led by Carles Puigdemont, the former Catalan president. After the 2017 independence referendum, Puigdemont fled in a dramatic police chase one night, in which he changed cars under a bridge. He now lives in Belgium as a Spanish MEP. Spain issued an arrest warrant, but Belgium could not extradite him because Spain's official charge of "rebellion" has no equivalent in Belgian law.

Last July's Spain's general election produced a hung parliament. The opposition Popular Party came first, but did not have enough allies to form a coalition. The Socialists and the regionalist parties agreed a confidence and supply deal, which included an amnesty deal for Catalan politicians arrested after the referendum.

There are not many western European countries where political parties agree to overturn prison sentences. The amnesty deal prompted a complaint from the European Commission, which expressed concern that it might violate European rule-of-law procedures.

The toxic interaction between law and politics goes both ways. Spanish courts regularly ban politicians from holding office, as happened to Quim Torra, who succeeded Puigdemont as Catalan president in 2018 after a short interregnum of direct rule by Madrid.

The EU and the UN are also alarmed by Spain's failure to renew the mandate of the general council of the judiciary, which expired in 2018. The general council is responsible for appointing judges, but appointments to the council require the consent of both houses of a politically divided parliament. The UN's special rapporteur on the independence of judges and lawyers concluded that the failure to appoint members to the council was hindering the functioning of the Spanish judiciary as a whole.

Spain's political divisions go back a long way, to the creation of modern Spain in the late 15th century. In 1469, the core of modern Spain emerged through the marriage of Isabella of Castile and Ferdinand of Aragon. This was the reign during which Spain reconquered Granada after the Muslims had been in control of the southern part of the country for almost 800 years. This was also the era of Christopher Columbus and the beginning of Spain's colonial empire.

Spain's glory days coincided with the fall of Catalonia. During the middle ages Catalonia was one of the most successful principalities in Europe, rivalling Venice and Florence. What intruded was the Black death in the 14th century that affected Catalonia much more than mainland Spain, and led to a decimation of its population. Politics also turned against the Catalans. In his book Imperial Spain: 1469-1716, the late British historian Sir John Elliot reported that despite the merger of the two kingdoms, Catalans experienced discrimination in Castile, and as a result looked more towards the eastwards to the Mediterranean than westwards to the Spanish hinterland. Elliott concluded that Isabella and Ferdinand "had united two Crowns, but had not even tentatively embarked on the much more arduous task of uniting two peoples." A politically united but culturally fragmented country was a legacy that persists until today.