MI5's would-be spies

Britain's Security Service, more commonly known as MI5, marked 100 years of operations this week.

Its remit includes the protection of British interests, counter-terrorism and counter-espionage within the UK.

Although much of its work remains shrouded in secrecy, recent years have seen more open engagement with the public.

Part of this approach has included the open advertisement of MI5 roles in newspapers.

Although not targeted at children, these adverts have caught the eye of some keen youngsters who have written MI5 offering their services.

The BBC's David Whitty's report begins with some extracts from those children's letters.

First broadcast 7 October 2009