Cressida Dick, the Metropolitan Police Commissioner chats to armed officers as she walks along the Southbank in London, Britain, September 16, 2017. [Photo/Agencies]

LONDON - A home-made bomb which injured 30 when it partially detonated on a packed London train a week ago had the potential to cause much more damage, the head of the city's police force said on Friday.

The bomb engulfed a train carriage in flames at Parsons Green underground station in west London last Friday, in Britain's fifth major terrorism incident this year.

Six men have been arrested in connection with the attack, and four remain in custody.

"That was a very very dangerous bomb. It partially detonated, it had a large quantity of explosive, and it was packed with shrapnel. So it could have been so much worse," Cressida Dick, Commissioner of London’s Metropolitan Police, said in an interview on LBC radio.

She said that six militant plots had been foiled over the last several months.