What's most stupid about security for rail passengers is that the original fear from 9/11 doesn't even apply - you can't hijack a train and crash it into a skyscraper!
London had terrorist attacks from the IRA long before 9/11, including attacks on the transport network. There were 13 in 1991, of which 4 were on trains or at stations.
The new delays are for the passport checks. What used to be ~10 seconds for each EU citizen — is the passport/ID card valid and does the face match? — is now 60+ seconds for British people entering the EU, as the official must check they haven't stayed more than 90 days in the last 180 etc.
Hint when they ran a BART feeder to SFO the first thing the TSA did was start patrolling BART with drug dogs and arresting people for having pot.