Now we come to train 3. As far as I can make out, you found out at an early point (presumably on arrival on train 2) that train 3 had been cancelled,and you very sensibly did not hare across to wherever train 3 should have departed from only to find out that it wasn't there. So we cannot be certain whether you would - or would not - have caught train 3 if it was running on time.
I can be certain I would not have caught train 3. As train 2 was delayed and arrived with less than the minimum connection time, by the time I had walked over to the platform for train 3 (no dawdling, but no running) it was after its scheduled departure time.
Interesting to hear thoughts but can't say I agree with the reasoning.
Anyway, given the unreliability of these services which I now have to use regularly (looking at the recent service records I can't find a single day when the minimum connection time has been met by train 2 and train 3 has rather a habit of being suddenly cancelled), so I can easily see the alternative scenario of train 2 being delayed again and train 3 leaving on time, but the following train 3 (1/2 hour later) being cancelled.
From what has been said I think we can agree train 2 is definitely liable for the first 1/2 hour delay in this situation, but do they just have to suck up that the delay is now an hour? Or is it two claims, one each for trains 2 and 3? Or is train 2 off the hook and train 3 now gets to pay for the whole hour delay?
I can see some interesting correspondence ahead.