MANO PO is one way of expressing your high respect. This is almost forgotten by our new generations.
Before, If we have boyfriend or girlfriend that we like to introduce to our parents, lolo and lola's, we do mano po to them. If they don't want to lay their hands, that means they are not ready to accept you.
If there's wedding celebration, we usually see this mano po. The bride and grooms are doing this, and you can hear their whispers : Bless you, kaawaan ka ng Diyos.
I believe that if British BF and hubby's do this, your filipina girlfriend/wife as well as YOU will receive compliments from the old members of the family.
