An explosive device has detonated inside a teacher's car outside a school in Liverpool.

The blast happened outside Runnymede St Edward's in Sandfield Park, West Derby - an independent Roman Catholic school.

Although witnesses had said the device was a nail bomb, police described it as a small improvised firework.

Supt Ian Pilling described the incident as a "despicable". He said children were leaving at the time and it was lucky no-one was injured.

Roads around the school, which is a few miles outside the city centre and has annual fees of around £5,000, have been cordoned off by police.

A 21-year-old man arrested on suspicion of causing an explosion at a Merseyside school has been bailed pending further police inquiries.

The blast, caused by what police said was an "improvised firework-type device", occurred just before pupils began leaving for home on 21 September.

The device had been left in a teacher's Nissan Micra at Runnymede St Edwards school in West Derby, Liverpool.

No one was hurt in the incident, which police described as "a despicable act".

Runnymede St Edward's is a Catholic independent school for boys and girls between the ages of three and 11, and is Choir School to the Metropolitan Cathedral of Liverpool.