Seems very strange to try and abduct a serviceman in an area likely to have (armed) patrols with the Security state being 'Severe' isn't it?
https://www.mi5.gov.uk/threat-levels
If they were waiting for a 'random' runner rather than a serviceman/woman or a member of a service family returning home, wouldn't you do it somewhere a bit more off base?
I know we can't always look into the mind of a 'terrorist' however they can't be that ignorant of the risk of being caught that they'd wait on base rather than down a country lane ... can they?