It is a tale of private eyes, politicians, multi-millionaire football players, hip-gyrating Colombian pop stars and microphones hidden in posies of flowers.

At the centre of the blossoming scandal engulfing Barcelona's great and good lies a once ubiquitous detective agency, Metodo 3, whose safe full of secrets about the glamorous Spanish city's sordid underbelly is threatening to spill wide open.

As Spain's economy crumbles in the face of recession and austerity, Metodo 3 has joined the long list of companies to have closed its doors. Angry former employees have sought revenge by leaking some of the dirty tricks allegedly carried out on behalf of political parties and, now, the city's most famous soccer club, Barcelona FC.

The latest alleged victim of the agency's spying is the Barcelona and Spain defender Gerard Piqué, who was reportedly trailed on the orders of club bosses worried about whether his romance with the Colombian pop star Shakira and his embrace of the city's nightlife was damaging his form on the pitch.

The news website El Confidencial reported that the club asked for Piqué to be followed in 2010 in order to see how much time he was spending partying. It says in September 2010 Piqué was trailed after going to a pop concert in Barcelona. Detectiveslogged the drinks he had and the time he got home. El Confidencial said the player eventually realised he was being tailed, but the club managed to persuade him that it was just the tabloid press.

The club issued a confusing denial. "The club does not wish to comment on this because it has no documentary evidence that this ever happened and, as a result, we deny it," a spokesman said on Tuesday.

Although rumours that the club had spied on numerous players – including former stars Samuel Eto'o, the Brazilian Ronaldinho and Portugal's Deco – have circulated for several years, it is the first time that Metodo 3 has been named as the agency that allegedly carried out the work.

The agency's political activities first came to light in published recordings of a lunchtime conversation between a local leader of prime minister Mariano Rajoy's People's party (PP) and the angry former girlfriend of a businessman closely connected to the Catalan Democratic Convergence (CDC), the party that governs Catalonia. A microphone hidden in a centrepiece posy of flowers reportedly captured her tale of alleged money-laundering in Andorra and London.

Barcelona FC's former head of security Xavier Martorell is one of the key players in the scandal. Now head of Catalonia's prison service and a senior CDC member, Martorell has admitted hiring the agency to do work for the party. He is even reported to have requested reports on people within the CDC, though he strongly denies these allegations.

However, it seems most other major political parties also hired the agency. PP secretary-general María Dolores de Cospedal has admitted using Metodo 3, and former agency employees say they also worked for the Catalan branch of the socialist party. All say there was nothing illegal about the tasks the agency was asked to perform.

Police last week raided the agency's offices in Barcelona and Madrid and removed files, leading to speculation that they were now privy to secret reports on many of the most important people in the city.

Already Catalan politicians are claiming the government wants to get its hand on the documents as a way of gathering information on them and blocking moves towards independence. The head of Spain's CNI espionage service, General Félix Sanz Roldán, has publicly stated that his agency is not involved.