The Day Before it All Happened

Very interesting comment worthy of a post and following up from the eye witness accounts on the BBC News web site which refers to armed police activities going on yesterday on the route of the number 30 bus, the route of the bus that happened to be involved in today's events:

Yesterday late afternoon, my partner and I drove back through London after a mini-break to Brighton rather than face the M25. Hackney seemed to be crawling with police cars and I even saw an armed officer patrolling the streets, which seems ironic considering the bus involved in the blast at Tavistock Place has been reported as the number 30 Hackney to Marble Arch service.
Kelly, London

Source: BBC News - London Explosions Your Accounts

What was all this armed police activity on the number 30 bus route the day before a number 30 bus appears to have exploded in a 'coordinated terror attack' on London?