I know that people are notoriously bad at understanding probability but he just needs to look at the facts.
There are about 4 million public transport journeys everyday in London and 8.6 million residents plus all the tourists at this time of year. If your DH screws his rational/probability head on what are the chances of anything happening to DS? Compared with crossing a road, having a car accident, slipping on a wet bathroom floor, falling down stairs, having a sports injury, falling over in a playground.....
In the UK there have been an average of 1.4 deaths per year from terrorism in the past 10 years (including this year). Even within the last 3 months the death toll is 34 people. Much less than it was in the 1970s - at the height there were 350 deaths a year!
By contrast, every year there are approximately 6,000 deaths as the result of a home accident.
So on that basis - he's safer on the streets of London than in your living room! (Source: Office of National Statistics; ROSPA)
See this article: www.telegraph.co.uk/news/0/many-people-killed-terrorist-attacks-uk/
More from ROSPA:
More than two million children under the age of 15 experience accidents in and around the home every year, for which they are taken to accident and emergency units
Over 76,000 children under the age of 14 are admitted for treatment of which over 40% are under 5 years of age
Every year over 62 children under 14 die as a result of an accident in the home
More accidents happen in the lounge/living room than anywhere else in the home.
Every year more than 4,200 children are involved in falls on the stairs and 4,000 children under the age of 15 are injured falling from windows
Boys have more accidents than girls
The cost to society of UK home accident injuries has been estimated at £45.63billion (£45,630million) annually.