Two men with histories of mental illness were yesterday convicted of plotting to rob and murder the singer Joss Stone at her secluded Devon home.

A jury at Exeter Crown Court took just over four hours to unanimously convict Junior Bradshaw, 32, and Kevin Liverpool, 35, of harbouring such deep hatred for the international soul star that they conspired to behead her using a samurai sword and dump her remains in a river.

The pair were arrested in June 2011 as they drove along country lanes close to Miss Stone’s isolated house, raising the suspicions of a postman and several others by asking for directions in a car loaded with equipment, including balaclavas, an improvised body bag, knives and metal spikes.

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Liverpool, who had shared a flat with his co-defendant in the Longsight area of Manchester, was jailed for life following a three-week trial in which it was revealed he wrote notes detailing the killing and criticising the singer for her links to the Royal Family.

Sentencing him to a minimum term of 10 years and eight months, Judge Francis Gilbert, QC, told Liverpool: “It was your scheme. This may have been the crazy scheme of a crazy person... but it was a very real plan.”

He added: “You intended to rob [Miss Stone] and kill her and dump her body in the river, according your words, and then leave the country with your accomplice Junior Bradshaw.”

Philip King, QC, for Liverpool, told jurors that the two defendants were “incapable, bizarre, deluded incompetents” who had embarked on a “frightening fantasy,” leaving their flat at 2am to make the journey to east Devon.

Bradshaw, who will be sentenced at a later date, has a history of schizophrenia which the trial was told meant he was incapable of taking part in any plot and could not be linked forensically to any of the weapons or notes. The 32-year-old suffers from a form of the mental illness which leaves him incoherent and disorganised with little awareness of the passing of time.

Bradshaw told his trial he thought he was “going on a day out” when he travelled towards Stone’s home and had never heard of the singer. But a forensic psychiatrist called by prosecutors said the would-be killer was well at the time of his arrest and was capable of organising his life.

Speaking after the verdicts, Joss Stone said: “I am relieved the trial is now over.”