With a few exceptions terrorists attack targets for their propaganda impact. Only rarely do they attack key national targets, although attacks on US embassies are the exception - since Beirut - as they are suicidal.

So there is a continuity over time, as Wilf cites from Israeli history and more contemporary attacks like Mumbai are alas an escalation. They remain armed propaganda, with all the real-time imagery that technology enables.

In the UK's recent experience the Provisional IRA did mount spectacular attacks like Canary Wharf in London, the Arndale Shopping Centre in Manchester and a M-way junction. All had an impact commercially, notably Canary Wharf. They also tried twice to kill the key members of the UK government, with the Brighton hotel bomb and No.10 Downing Street with mortars - both times nearly killing the cabinet.

I am sure there are other "near misses" on key national targets, so I await how the discussion goes.