MOSCOW — British rock musicians have called for a fair trial for three members of Russian punk band Pussy Riot, jailed for the past five months after staging an obscenity-laced protest against president Vladimir Putin at a Moscow cathedral.In a letter published in the London Times Thursday, rock stars including Pete Townshend, Jarvis Cocker, Alex Kapranos of Franz Ferdinand and Neil Tennant of the Pet Shop Boys write: “Dissent is a right in any democracy and it is entirely disproportionate that they face seven years in jail for what we consider a preposterous charge of ‘hooliganism motivated by religious hatred.’ “ Timed to coincide with Putin’s arrival in London, the letter is the latest in a string of high-profile protests by artists and performers. The trial against Nadezhda Tolokonnikova, Maria Alyokhina and Yekaterina Samusevich started Monday at Moscow’s Khamovnichesky Court. The trio were initially released without charge after the protest. They were arrested later after complaints from the head of the Russian Orthodox Church, Patriarch Kirill, indicating the increasingly close ties between church and state. British prime minister David Cameron, who met Putin Thursday, was expected to raise the trial as part of a wider conversation on human rights in Russia.