Since you could probably be shown to be able to prevent the theft by the use of
a) Shouting to make them fuck off or
b) grappling to remove them from the bike
The additional use of a weapon is unlikely to be reasonable unless the thief actually threatens you or someone else with personal harm.
Since you could probably be shown to be able to prevent the theft by the use of
a) Shouting to make them fuck off or
b) grappling to remove them from the bike
The additional use of a weapon is unlikely to be reasonable unless the thief actually threatens you or someone else with personal harm.