A particular person wanting to travel is barred for entry to the UK. This means if they set foot on UK soil they will be arrested and put in jail.
This is all ok, however there are a number of good flights which transit through the UK.
Would this person get arrested upon landing in the UK, even though the airport is technically not the UK and they are transiting within a few hours?
This is assuming they do not cross the point of immigration of course.
This is based on the assumption the person travelling committed a crime and has been explicitly barred from entry to the UK.