I'll try, off the top of my head,
1. No hand luggage at airports,etc, (see www.open.gov.uk
) Be aware, but carry on as normal.
2. Airport police openly carry automatic weapons. (Our police are not routinely armed, excepting Northern Ireland.) All baggage x-rayed, If you miss the flight your bags come off before it leaves, metal detectors in important buildings, Most larger towns have cctv cameras in town centres.Gradual build-up over the last 30 years, so it's hard to remember what it was like before, it's just "normal" Airport security I suppose, started in the 70's with hijackers. Mainland security is mostly anti- IRA. They tended to set bombs, and telephone mostly accurate warnings before, though not always. Of course in N.I. the army were/are on the streets, there has been a ceasefire now nearly 3 years, but splinter groups are still active, eg Omagh, much less so since Sept 11 and there is talk of the IRA actually giving up weapons. As to good or bad, things were almost tit for tat, until the politicians started talking with them. Shooting people makes martyrs for the cause, and although these "Troubles" have lasted 30 years, the reasons date back nearer 300!
3. At work there are critical incident procedures, for mass casualty accidents etc, included within that are bomb alerts, and the like.
4. I had to think on this one. I suppose I am a little more on the alert for unusual / suspicious packages, or behaviour, but don't feel directly affected, not living in a high risk target sort of area. In London, I might well more at risk, so I would only go there if really necessary.
5. Nothing on this one really, they and their families have had the same general, non specific warning from the Govnt.
One thing occurs to me! this panic over gasmasks, weird! Being sprayed with toxic gas is highly unlikely, due to the practical difficulties involved in distributing the stuff without the terrorist killing themselves first. If those around you start falling down, then it's probably too late anyway, and like wise with infectious agents. By the time people are becoming sick, it will be a day or two after they got infected, so gasmasks will be useless. IMO