An unemployed 48-year-old divorced British father is now detained in France for admitting the murders of his two very young children by slitting their throats, abruptly terminating what could have been the start of a series of father-children bonding moments without a third party.

Julian Stevenson, 47, admitted to killing his 5-year-old daughter and 10-year-old son. Arrested on Saturday night in Lyon, he is expected to appear in court in France on Monday to face formal charges with slitting the throats of his two young children.

It remained unclear as to what prompted Mr Stevenson to do the gruesome acts on his very own children, who were entrusted to him for the first time again by his French wife ever since their separation.

Mr Stevenson "did not go into details of the motive," prosecutors were quoted on Sunday. A knife believed to be the murder weapon had been recovered from the crime scene.

The bodies of the children were discovered in a flat near Lyon, where Mr Stevenson lives. It is believed it was the mother, who had gone to her former husband's flat to pick-up the children after Mr Stevenson failed to return them to her, who discovered the bloody scene when she arrived at his flat on Saturday afternoon. Reports said she found her former husband in blood-stained clothes, standing on the stairway.

Upon seeing her, Mr Stevenson immediately fled on roller skates.

His former wife, an assistant accountant, won custody of the children following their divorce. She and the two children left their family home to live in Isere, a region to the south-east of Lyon.

"We understand that a British national has been arrested in France," a Foreign Office spokesman told AFP. "We are in contact with the French authorities and we await the outcome of their investigation."