The 'White Widow' is thought to have been waiting for him and Brit Abu Talib in Kenya where she was planning attacks for al-Shabaab.

Talib was already under surveillance on suspicion of raising funds for the group. His link with al-Shabaab explains why he and Emwazi were held by security services while on holiday in Tanzania in 2009.

After being questioned, Emwazi flew to Amsterdam and was met by MI5. He was asked about terror links but returned to the UK. He went to Syria in 2012 where he joined IS.

Reports last year that Lewthwaite had been killed remain unconfirmed.

Emwazi also had links to the failed 21/7 London terror attacks, it has emerged.

The ISIS executioner was a member of a 12-strong terror cell which had connections with the four would-be bombers who planned to bring carnage to the streets of London.

On the day of the failed attacks, one leading member of Emwazi’s network chatted on the phone with Hussein Osman, who was later jailed for life for placing an explosive at Shepherd’s Bush tube station.

And associates of of the West London terror cell - set up in 2007 to recruit for al-Shabaab - had been at a training camp on Cumbria with the four 21/7 masterminds just a year before they carried out their plot.

The revelations, contained in secret court papers, have raised questions about how Emwazi was able to evade security services to slip out of the country in 2013 for Syria.

He had been on MI5’s radar for six years before he appeared on an ISIS hostage video for the first time in August 2014 when he apparently killed the US journalist James Foley.

He was later thought to have been pictured in the videos of the beheadings of US journalist Steven Sotloff, British aid worker David Haines, British taxi driver Alan Henning, and American aid worker Abdul-Rahman Kassig, also known as Peter.