A 26-year-old engineer is to appear in court on Monday following an incident in which a car ploughed into the security gates guarding Downing Street.

Stephen Bonnett, of Writtle, near Chelmsford, Essex, will appear before Bow Street magistrates in central London, said a Scotland Yard spokeswoman.

He was charged with causing grievous bodily harm to mother-of-three Ursula Webster, who was on holiday with her family from America, and with dangerous driving, following Saturday's incident.

Police were alerted when a red Vauxhall Astra smashed into the reinforced gates barring access to the Prime Minister's residence at 1231 GMT.

Mrs Webster, who is being treated in hospital for a broken leg, was walking through the gates with her family after being allowed to walk up to the famous Number 10 door when the collision happened.

Her three sons - aged three, six and eight - escaped the ordeal virtually unscathed as their mother, who was accompanied by her husband, sacrificed her own safety to push the children aside.

Downing Street confirmed the Prime Minister and his family were not in their home at Number 11 at the time of the incident - and said Mr Blair would be writing personally to Mrs Webster.

A spokeswoman said: "The Prime Minister and Mrs Blair were not in Downing Street at the time. The Prime Minister has asked to be kept informed of the lady's progress and he will be writing personally to her."

The ornate black and gold gates were erected as a security measure in 1989, on the orders of then prime minister Margaret Thatcher, and amid strong opposition at the time from Labour.

Former prime minister John Major and his Cabinet narrowly escaped injury two years later when an IRA gang fired three mortar bombs from a Ford Transit van in a nearby street.

One of the weapons landed in the garden behind Number 10, blowing out windows in nearby buildings.