A train would never be more than 30 minutes late due to passengers taking a long time to board the train.

I find that with some Northern services that are run by 4 carriage trains the conductor is still checking tickets when the train arrives at the station and it takes him 2 or 3 minutes to get to the end of the train and open the doors after the train has stopped.

Yes I've noticed that myself.
I can, to some extent, appreciate why the driver doesn't usually close the doors but why can't he/she open them? The driver is the best person to know if the train has safely stopped.:confused:

On some trains particularly 142s I think the driver would have to leave the cab to open the door, so it wouldn't be time saving on the less busy trains.

I was implying that, on multiple units, the necessary switch should be placed in the driving cabs to enable the driver to unlock the doors. Where this isn't already the case I can't see it being a particularly complex or costly modification to make, even on a 142.
In mainland Europe the doors on similar trains are opened and closed by the driver aided by nothing more than a rear-view mirror.

On some MerseyRail Class 507 and 508 trains it's like that. Conductors are not present on every train and there are no open or close buttons by the door. If conductor(s) are present then they open or close all the doors, otherwise the driver does it.

Compensation from VWC and GNER
 

When I was living & working in N. London, I once travelled from Watford Junction to Edinburgh. It was in late August 2001, and I planned to get a VWC train leaving WJ at about 1345. It transpired that something had derailed in/around Wembley, preventing anything arriving at or leaving Euston (except the DC trains). The scheduled train eventually turned up 90 minutes late, but as we sped through Milton Keynes, the guard came round handing out leaflets explaining how to claim compensation. I used it and got a £42 voucher back on an £85 ticket, which I used on a GNER train a month later. For 2 years after that, I regularly (but legitimately) claimed compensation from GNER and they willingly coughed up. However, I had to get a form from the Kings Cross ticket desk - they were never volunteered on the train nor by staff wandering about the station. One thing fascinated me at the time - EVERY compensation voucher I received was to a value that was a factor of £21 (£21, £42, £63, etc). In the 2.5 years I used GNER, they compensated me a total of £231.