TTT
First, I would support the expansion of anti-terror legislation so that 'enhanced monitoring capabilities' were easier for the security services to roll out.
Once credible information (not threat, but information) was obtained - immediate arrest and detention.
Under the provisions of this new anti-terror legislation, suspects can be held (upon judicial review of the case) for six months whilst security services assess the threat based on a new set of protocols, which would have to be ratified by Parliament.
This would mean a wholesale upheaval in our judicial process, but lets be honest - I think that a) most people would support it and b) it's only going to affect would be terrorists.
Also, I would put a penny on income tax to fund an increase in police and security services numbers.
And I commission a public inquiry into our trade, economic and military relationship with all areas of the Middle East.