A 17-year-old boy who caused £40m of damage to the economy by throwing firebombs on to a motorway, causing a 12-hour closure, has been made subject to an interim hospital order.

In a hearing at Winchester crown court on Monday, the judge, Keith Cutler, described Nicholas Elger as a “dangerous young man”. Elger, from Winchester, threw petrol bombs on to the M3 on two occasions in September 2017.

Cutler ordered that the defendant continue to be treated and assessed at a psychiatric unit, but warned Elger he faced a significant custodial sentence if his condition was deemed untreatable.

The judge lifted an order banning the teenager’s name being reported, saying it was in the public interest for Elger, who attended the private school Winchester College, to be identified.

Elger, who admitted “wanting to kill someone”, has pleaded guilty to two charges of arson.