A British terror suspect on the run in Africa plotted an armed assault on a Kenyan courthouse to free her accomplice from custody, lawyers have claimed.

Samantha Lewthwaite, widow of one of the 7/7 London bombers, is reported to have hatched a plan to free terror suspect Jermaine Grant before or during his court appearance.

Grant, from Newham, east London, is on trial accused of planning explosive attacks across Kenya. It has been alleged that he was working with Lewthwaite, the widow of the 7/7 Kings Cross bomber Germaine Lindsay.

Prosecutor Jacob Ondari urged Mombasa magistrates to move the trial to a high-security court complex because of the reports of a violent attempt to free the defendant.

Ondari said that Grant's co-accused, Fouad Manswab, who was also on the run, worked together with Lewthwaite to hatch the escape plan.

Lewthwaite has been on the run for 15 months. She faces the same charges as Grant and Manswab, which include conspiracy to improvise an explosive device with the intent to cause harm to innocent civilians.

Ondari said after the first hearing: "There is evidence that associates of the first accused masterminded a plot to free him from custody.

"We believe the group secured weapons and planned a violent attack on the court or on vehicles used to transport him from jail.

"It is believed that the Samantha Lewthwaite was among the group. We believe she would have been involved in the rescue mission, which was foiled by police."

Ondari added that one man was arrested in Mombasa with a grenade and another was stopped from crossing the Kenya/Tanzania border in possession of bullet-proof vests and facemasks. Both men admitted to being part of the plot to free Grant.

Lewthwaite, from Aylesbury in Buckinghamshire, is also suspected of helping to fund terror groups in Kenya.

She was questioned by police in December 2011 but escaped along with her three children. She is believed to be in Tanzania or Somalia.

Grant and Manswab were arrested in December 2011 after chemicals were found in their flat identical to those used by Lindsay in the cordinated London terror attack which left 54 people dead.