DAMIEN HENDERSON and MARTIN WILLIAMS

A PRIVATE investigator was arrested yesterday in connection with a stolen Leonardo da Vinci masterpiece recovered earlier this month.

Mike Brown, who runs a detective agency in Glasgow, is the fifth person to be detained in connection with the art theft, described as the UK's biggest.

It follows the recovery of the 500-year-old The Madonna with the Yarnwinder, which has been valued between £15m and £40m, during a raid on a Glasgow solicitor's office on October 4 in which four men were arrested. The Leonardo was taken from Drumlanrig Castle, near Thornhill in Dumfries and Galloway, in August 2003.

Mr Brown, 45, was arrested by Dumfries and Galloway Police at his home in the south side of Glasgow and taken to police headquarters in Dumfries. He is expected to appear at Dumfries Sheriff Court today charged with conspiracy to rob and extort money.

Mr Brown is the director of Diamond Investigations, which he set up in 1990 and runs from offices in Charing Cross, Glasgow.

The company's website describes a "professional, discrete and completely confidential service" and says its areas of investigations include matrimonial inquiries, stock theft, vetting potential employees and employee sickness fraud. It claims to have banks, local authorities and legal services among its clients.

In an interview with the Evening Times in 1997, Mr Brown also claimed he charged between £60 and £100 an hour to act as a "male decoy" in order to find out if his clients' wives or girlfriends were prepared to have an affair.

There was no reply at the offices of Diamond Investigations when The Herald called yesterday afternoon.

At his high-security gated home in Haggs Road, Pollokshaws, where Mr Brown is understood to have been arrested, a woman believed to be a relative said she "knew nothing" of what had happened to him before refusing to comment any further.

A police spokesman said: "Officers from Dumfries and Galloway Constabulary arrested a further fifth man in relation to the ongoing Madonna with the Yarnwinder investigation. The 45-year-old man from the Glasgow area will be appearing at Dumfries Sheriff Court tomorrow in connection with this crime."

Four men appeared at the same court earlier this month and were released on bail. Calum Jones, 52, from Kilmacolm in Renfrewshire appeared alongside three men from Lancashire: Robert Graham, John Doyle and Marshall Ronald.

Mr Jones resigned on Friday as a corporate partner with HBJ Gateley Wareing following his arrest and the recovery of the Leonardo from the firm's offices in West Regent Street, Glasgow.

The picture belonged to the Duke of Buccleuch, who died in September at the age of 83. The picture had been in his family for two centuries and was admired by thousands of visitors to the castle every year.