The patronising suggestion that a terrorist is thick enough to need this incident to give them an idea is laughable.
All they have to do is blow themselves up outside the stadium as fans arrive.
This isn't the IRA circa 1982.
I'd like to take this opportunity to apologise to all terrorists for implying they may be stupid*
*Like none of them ever set fire to their own underpants and genitals.
I'd go as far as to suggest that many terrorists (or would-be terrorists) ARE stupid.
It's incredibly easy to cause maximum disruption to a western city, with minimum risk and with out that much loss of life actually.
I'm actually surprised that there aren't daily events/disruptions.
4 people and 4 empty, but "suspicious", Transit vans, and one phone call, could gridlock London for 24 hours.
No loss of life but huge disruption and publicity.
"Just blowing yourself up" involves explosives, and that raises the game significantly.
The security forces will have undercover operatives monitoring that level of activity. That's why they keep finding "Bomb Factories".
Almost every incident involving Bombs and guns also involve people being monitored (OK, unsuccessfully) by security forces. That implies they know the "hard-liners".
It's actually reassuring how few incidents there are. It tells me this isn't a war with Islam, it's a war with just a few nut-jobs.