I very much doubt the 20 seconds!!!
The existing security you would be lucky for one passenger through every 1-3minutes with how they operate at LHR!
I was asked to go through the body scanners twice when they were being trialed, & it was at least 5 minutes.
I still think profiling of passengers & an equivilant security certification (based on patterns of travel, FF status as being known to airports or Airlines, Immigration history, ticket sourcing -cash vs cards, single vs return tickets etc) is the way to go.
If you make the trip regularly on a route with an Airline, as many BT readers do, you should be given a reliable higher known security status.
It is not viable to put everyone through body scanners for every flight out of the UK, or other countries. Clearly there will be less resourced countries who will not have them, & still many Airlines will fly passengers into the EU Airports, where this level of security cannot be matched.
This is precisely what happened in the recent incident.
Could LHR also perhaps check passports as you travel out of LHR?
I have not had mine checked for 2 yrs out of T4, even travelling every 2 weeks!!! Really NO point having immigration systems, if you don’t know who has left…it’s simply common sense???
Schipol have passport checks at every gate prior to boarding, separate from security, as well as entry to the airport & the Airline itself.