It depends what you count as political reasons. Plausible bullshit could be generated to support the idea that arrest for any particular crime is political, or just as easily, to oppose that idea.
I draw the bar for "political arrest" at somewhere like "arrested for opposing the incumbent in an election". I don't think "arrested for saying it's time to gas the muslims" - which is the sort of thing happening in the UK and getting counted in these numbers - should be called "political arrest". That's just called committing a crime. That would only become a "political arrest" if gassing the muslims was a politically acceptable viewpoint, equal in value to not gassing them.
I draw the bar for "political arrest" at somewhere like "arrested for opposing the incumbent in an election". I don't think "arrested for saying it's time to gas the muslims" - which is the sort of thing happening in the UK and getting counted in these numbers - should be called "political arrest". That's just called committing a crime. That would only become a "political arrest" if gassing the muslims was a politically acceptable viewpoint, equal in value to not gassing them.