Advice for Boris

As soon as you win the election, demand all the backup media for the Exchange Server(s) at the Mayor of London's office. You want all the backup media as far back as possible, the last year end media, any media stored on-site, off-site or at a disaster recovery site. The truth as to what Ken Livingstone has been up to may be only on those media. If there are no backups then an immediate investigation is called for and remember there are people who can retrieve data from mangled media and emails deleted from Exchange.