Hundreds of extra armed officers are to be trained to help counter the threat of a terrorist attack in London, the Metropolitan Police is set to announce, BBC News reports.

It comes after Scotland Yard reassessed its ability to stop terrorism and respond to armed attacks in light of last year's deadly attacks in Paris.

Some 600 extra officers are expected to receive firearms training - in addition to 2,000 already trained in London.

Met commissioner Sir Bernard Hogan-Howe says he is determined to boost numbers. Speaking on LBC radio on Wednesday, Jan 13, he said there was likely to be a "significant announcement" on Thursday.

Prime Minister David Cameron has ordered a review of the use of guns by police in England and Wales, following the Paris attacks, which left 130 people dead.

Last month, Hogan-Howe said the number of armed patrols by the Met had risen by one-third and he wanted to increase that further.

UK counter-terrorism bosses also revealed for the first time that police marksmen were being told to walk over casualties and go forward to confront gunmen should there be an attack.

Outgoing City of London Police Commissioner Adrian Leppard also suggested the Army could be called in to man armed cordons if there were multiple gun and bomb attacks, as happened in Paris.

The number of armed officers across England and Wales fell by 1,000 from 2010 to 2014.

The Home Office has made £34mln available to improve police firearms capacity and help forces deal more quickly and effectively with a possible gun attack.