Michael Sandford, 20, of Dorking, Surrey, was due to appear in court on Tuesday charged with trying to grab a policeman's gun to attack the Republican presidential candidate in June.

But now, Lynne Sandford says, her son has agreed to plead guilty to being an illegal alien in possession of a firearm and disrupting government business when he appears in court later.

Mrs Sandford told ITV News London: "I was very relieved that he signed it.

"It was a bit of a battle because he is quite headstrong. 

"But we all laid the options out there for him on the table and, of course, it is a gamble."

Mrs Sandford has previously described her son as vulnerable, explaining he suffers from a number of mental health issues including autism, anxiety, depression and anorexia.

She says he would not have understood the consequences of his actions.

Mrs Sandford said of the deal: "There's no certainty. But he has signed the plea agreement.

"Now we have to wait to see if the judge will accept it and hopefully it's the end of one stage and the beginning of another stage.

"Every stage is a stage closer to him being able to come home."