Grace Mugabe, the first lady of Zimbabwe, returned home last night from South Africa after being granted diplomatic immunity after being accused of assaulting a model with an extension cable in a Johannesburg hotel.

However last night lawyers announced they would launch a legal challenge this week to the immunity which allowed Mr Mugabe to escape facing any charges of assault.

The immunity, granted after she arrived in South Africa more then a week ago on private business was a political decision not a legal one said Lorna Ferguson, a South African lawyer.

“It was irrational and in contravention of South African laws for her to be granted immunity in the face of what were serious criminal charges laid against her for alleged assault a week ago.

“I consulted the law and with a veteran South Africa foreign affairs expert who said that immunity cannot be granted retrospectively.”

Mrs Mugabe is accused of assaulting and injuring Gabriella Engels, a 20-year-old model who was visiting Mrs Mugabe’s two sons, Robert Jnr and Chatunga in a top Johannesburg hotel a week ago.

Ms Engels laid charges against Mrs Mugabe after she had her face stitched up in hospital.