On a technical note, I'm pretty sure that the Americans used guerilla tactics against the British in the War of Independence. Anyway...
I too believe there is a sinister agenda within the fundamentalist community of this country to actively terrorise British citizens.They skulk under the blanket of tolerance and freedom that Britain provides for its inhabitants. They prey on the defenceless and sometimes even kill them as demonstrations of power. Sadly, these idiots are racist twats who stir up violence and hatred under the guise of patriotism, and some of them even work for newspapers. In fairness, newspapers are usually more moderate... At the moment... But it only takes events like the July 7th bombings to rile them up and get 'kill the bastards' screamed from the headlines.
There's an old word for the fight against disruptive elements that are disguised inside society, when a few cause suffering to the masses: it's called policing. You don't go to 'War Against Murder', but I'd be willing to bet that there are more murderers in this country than active members of terrorist groups.
Yes, we do need to take these threats seriously, but by engaging with them on their level we also make terrorists win. The chances of dying in a road accident, or slipping in the bath, or suffering any other number of pointless sad deaths that we all face on a daily basis far outweigh that of terrorism and by giving those few who wish to scare us the honour of saying we're 'at war' with them glorifies their actions for the few sick enough to admire them. We have never stopped taking the threat of terrorism seriously, but we've always, until recently, kept it in perspective.
This 'war' is not a war. It's police work. The terrorists are happy to wait and pick off groups here and there, that what they've always done. The American troops fought a war against the British using the same tactics, and they won in the end because the British acted like they were at war. Look how that turned out, the Americans won. You can win a war against an enemy that's rarely there, you can only spend your resources chasing shadows. You certainly can't beat a war against an abstract concept like 'terror'.
Is it worth pointing out that America was founded by terrorists? Nah, probably not...

Perhaps an extra stipulation of the usual definition of war, that being 'armed conflict between two countries or two groups inside a country', should be that there is a way in which the war can end. A war against terrorism cannot end because it is defined by ideologies. Eventually anyone who disagrees with you becomes a terrorist, and so you create new threats: the war cannot end. If a war cannot end then surely it's not war, it's just life?