Not sure but I believe you may be in the Hemel Hempstead area somewhere. Do you have any idea how many mosques there are in the vicinity? If there's several it could be a way of crippling the UK without doing any damage to the mosques.
I'm far from there. I'm just reading FR and praying for our British commrades-in-arms (and for your daughter and son-in-law.)
Tell them to fill up their car with gas and get out of there till the area stabilizes.
Prudence is not a bad thing.