Speight, who hosts the show SMart, was arrested at the scene.
Sky News reported that Speight’s girlfriend Natasha Collins had been found dead in a bath.
A BBC spokesman had no immediate comment. Speight’s representative at the theatrical agent Billy Marsh Associates could not be reached immediately. But his lawyer denied any involvement.
“Mark was the only other person present in the flat and has therefore been questioned by police as a matter of course,” said lawyer Nabeel Sheikh, of London law firm Sabir Selby.
“He is assisting police with their enquiries 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.”
Speight has hosted the series Beat the Cyborgs and SMarteenies, and has made appearances on Blue Peter, The Saturday Show, The Heaven and Earth Show, and also the Saturday morning show Scratchy and Co.
UPDATE: Mark Speight has now been cleared of any involvement.