The BBC children’s television presenter Mark Speight has been arrested on suspicion of murder and supplying cocaine after his fiancée was found dead at their home.

The body of Natasha Collins, 31, an actress and model, was in the bathroom of the flat where the couple were living in St John’s Wood, northwest London. The police investigation has centred on a suspected drug overdose.

Mr Speight, 42, presenter of the BBC show SMart and a children’s favourite for more than a decade, said he was “absolutely distraught” at the death. He said that he had found the body and immediately called an ambulance and police. The incident comes days after the suspected drug-related death of Kevin Greening, a former Radio 1 breakfast DJ. A post-mortem examination revealed that he died in his sleep after taking large quantities of cocaine, Ecstasy and GHB.

Mr Speight was bailed by police on suspicion of murder and supplying Class A drugs. He is assisting police with their inquiries and has denied involvement in his fiancée’s death.

Mrs Collins acted in theatre, television and film after graduating from drama school. Her acting career was restricted seven years ago, however, when she was knocked down by a car and seriously injured.

She met Mr Speight when they appeared together in the 1999 CBBC show, See It Saw It. Mrs Collins played the jovial court jester to Mr Speight’s King. The rubber-faced Mr Speight, who appeared on the ITV Saturday morning show Scratchy & Co, became a fixture with young viewers, presenting SMart for 12 years. Regular TV roles dried up for Mrs Collins, who worked as a model and presented corporate videos. Colleagues praised her “professionalism, bubbly personality and beautiful looks” yesterday, but observers noted that she was “painfully thin”. The couple had been engaged for about three years.

A statement released on Mr Speight’s behalf said: “Mark has been questioned by the police on account of the fact that the body of his fiancée, Natasha Collins, was found in the flat they shared.

“At the moment no one knows what happened. Mark found her body in the bathroom and immediately called an ambulance and the police. He is assisting police with their inquiries and had nothing to do with Natasha’s death.

“Mark is absolutely distraught at the loss of Natasha and hopes that everyone will appreciate what a very sad time this is for both Mark and Natasha’s family.”

A Scotland Yard spokesman said: “Police were called at 13.20 on January 3 to reports of a sudden death of a woman at a residential address in St John’s Wood. The woman, aged 31, was pronounced dead at the scene.

“A man in his forties was arrested at the scene. He has been bailed to return to a Central London police station on a date in early February.”

The death was being treated as “unexplained”, he added. Police had ordered toxicology tests to determine how Mrs Collins had died and a post-mortem would take place next week.

The BBC has cancelled today’s scheduled 10am showing of SMart. Repeats of the show are being screened on CBBC. A BBC spokeswoman said that a decision had yet to be made on whether next week’s episodes would be shown. A new series of SMart is not scheduled until the end of the year.

Mr Speight had just finished performing in a production of Cinderella at the Watersmeet Theatre in Rickmansworth, Hertfordshire. He copresented shows with Rolf Harris and appeared on Blue Peter, The Saturday Show and The Heaven and Earth Show.

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