Now, even though there is a great mass of 17th century documentation about the Gunpowder plot, it is still quite hard for me to grasp what pushed Guy over the edge?

What turns him from being a rebel who wanted change into an absolute radical willing to kill?

I'm intrigued if modern knowledge of extremism can help me understand the lengths to which Guy was willing to go.

So I've enlisted the help of a journalist and author who has written extensively on terror and particularly Al-Qaeda.

Jason, why do you think the plotters go abroad to recruit Guy Fawkes?

Because it's abroad that they'll find exactly the person they need.

The one thing that's really clear about more recent plots and those in the last few decades is that spending time back is absolutely crucial.

If they're overseas or, in fact, if they are just a long way from home, they can be kept in an environment where the radicalisation process is really very intense.

There are no other influences getting in: it's just the group, the ideology, the other people in that group.

Someone who was involved in terrorist training has said to me once that the only way that he could take a teenager and turn them into the kind of extremist actor that he wanted was by taking them away from their home and you put them in a kind of camp somewhere in a particular environment where you're surrounded by people who are committed to the same cause.

That will work.

I mean, he said to me, if I go back to their Mum every night, forget it.

That's not going to happen.

If they are in an environment that's outside their own kind of domestic environment, then you can really see that the radicalisation processes will happen quite fast.

Do you think it's significant that Guy Fawkes himself had been working as a soldier?

Yeah, very much so.

In that real kind of hothouse environment, his commitments and his tolerance for violence also will be reinforced, get higher and higher and higher.

So I think it's really important that he was he was what we would now call a foreign fighter.

He'd got skills, got psychologically hardened there, was exposed to some probably quite traumatic experiences and then came back and he's absolutely perfect to fit into this plot that is pre-existing.

Jason, do you have any insight into what makes a person willing to go all the way and kill loads of people?

The whole thing about terrorism is it's not a science.

What you can say is that whoever does it needs to believe that it is the only thing they can do in those circumstances.

They are very often seeing their community: the people they identify with as under threat.

Now that might be wrong...often is, but that's what they see.

And then that then justifies what they think they have to do.

No alternative.

There's no alternative.

It is now.

It is urgent and they have to be the ones who will do it.