Train passengers face routine airline-style bag checks and body searches as part of a new counter-terror crackdown announced by Gordon Brown.
He conjured up visions of ''Fortress Britain" as he unveiled a succession of security measures at airports, railway stations, sports venues and other public places.
There is also to be a huge "hearts and minds" drive aimed at diverting young Muslims away from the influence of fanatics.
The Prime Minister said a review of vulnerable buildings and crowded spaces like shopping centres had led to a rethink of the way they are protected.
More than 250 busy railway stations, airports and seaports as well as 100 "sensitive" installations like power stations and electricity substations will be given extra security.
This could include screening luggage at major stations like London King's Cross or Manchester Piccadilly using mobile checking devices that can be moved around the country.
More buildings will be defended by barriers to stop car bomb attacks, extra blast-proofing, vehicle exclusion zones and metal detectors.