I haven't watched it (I'm not sure how to not living in the UK). But you're 'main question of intent' seems wrong to me.
I've chased after thieves a few times in the past (in the UK). A couple of occasions come to mind - where i have caught up to them. One, as a countryside contractor, 2 guys had gotten into the works' van a few hundred yards away, I shouted and they ran, and I went after them. Ran across fields and eventually caught up to them. I was so out of breath I struggled to speak. They said they hadn't taken anything, and had just tried the door 'out of curiosity'. I was telling them it wasn't a good idea just as my mate came barrelling round the corner in the Landy scaring the sheet out of them - and they were off again. Another time, I was having a haircut and some scrotes came in and took the till. The staff were upset and quite at a loss and I went out after the thieves. Took the first one fairly quickly, grabbed him and shouted at him to stay put, which he did. And went after the rest - which, to cut it short, got away.
I think the first time i went after thieves was when i was 10. My brothers were 9 and 7. We were around our school in north Manchester and we saw 2 kids about my age passing stuff through a window at the school. We chased them off and I hopped in through the broken window, to what turned out to be the school office, and phoned the police.
Getting back to the point. There was possibly very little intent or forethought. Perhaps only a gut reaction to wrongdoing.