Baron Nazir Ahmed of Rotherham, Britain's first Muslim peer, and Baroness Sayeeda Warsi of Dewsbury, the Shadow Community Cohesion Minister, will lobby Sudanese leaders today on behalf of Gillian Gibbons.

Their visit comes as thousands of protesters gathered outside the presidential palace in Khartoum to demand a harsher sentence for Mrs Gibbons, 54, imprisoned on Thursday for 15 days after allowing her primary school pupils to name a teddy bear Mohammed.

The mother-of-two was moved to a secret location for her own safety after crowds, spurred on by radical clerics preaching at Friday prayers, became incensed that she had escaped a public flogging.

Last night Mrs Gibbons appealed for tolerance in a telephone conversation with her son – her first remarks since being detained.

Her son, John, said she appeared to be in good spirits.

"She just doesn't want any resentment to Muslims," he said outside his house in Liverpool. "She doesn't want people using her and her case as something to stoke up resentment towards anyone, towards Sudanese people, towards Muslim people or whatever."

Massing in central Martyrs Square for an hour yesterday, protesters burned pictures of Mrs Gibbons and chanted, "Shame, shame on the UK" and "No tolerance: Execution" and "Kill her, kill her by firing squad".

Protester Yassin Mubarak, swathed in green and carrying a sword, said: "It is a premeditated action and this unbeliever thinks that she can fool us? What she did requires her life to be taken."

He added: "The march today is meant to send a message that whoever plays with our religion and faith will bear the consequences."

During Friday sermons, the Muslim cleric at Khartoum's main Martyrs Mosque denounced Mrs Gibbons, saying she intentionally insulted Islam.

"Imprisoning this lady does not satisfy the thirst of Muslims in Sudan," said the cleric, Abdul-Jalil Nazeer al-Karouri, a well-known hard-liner.

The Foreign Office last night confirmed that Lord Ahmed was leading a delegation, saying it was a "private initiative".