My personal take (and I appreciate the sensitive nature of the situation) would to have rebuilt the towers exactly as they were as soon as possible.
It would have been the ultimate signal to whoever was responsible that whatever they hoped to achieve had failed.
Over here two raised fingers means more than just victory and the two towers reborn would have been the ultimate tribute to the resolve of New Yorkers and defiance of Americans against those who wish to oppress them.
Over here we got more CCTV cameras, pointless and probably counter productive security measures in airports, millions wasted on a scrapped ID cards scheme, de facto militias arresting people for taking photographs in public spaces and involvement in at least one war with people who had nothing to do with the attacks against the will of the countries that make up our Kingdom.
None of this happened when the IRA were shooting and bombing us on a weekly basis, and the few sacrifices to personal freedoms we had to endure when the Nazis were raining hell on our cities for eight months were returned to us immediately.
The whole response to this terrible crime stinks as much as the crime itself.