Euston - Watford Junction: Driver Only Operation

The Watford to Euston DC services have been DOO since 1988.

In response to the can the other lines be operated this way. The answer is yes they can al trains built since the 1980s are extensively made with DOO in mind.

That is why driver is king!

OPO = One Person Operation = London Underground's term
DOO = Driver Only Operation = National Rail's term (presumably inherited from British Rail)

They're essentially the same thing though. The difference may be due to the fact that the person in the cab at the front of the train is a "Driver" on National Rail trains but a "Train Operator" on LU ones.

In the Middleton Press book about the St Albans Abbey line, it says trains are crewed by three staff. Driver, guard and ....? Anyone know who the third member of staff would be? Is it something to do with setting points?

The only planned ATO sections are crossrail and thameslink and only in the central sections. No Plans for NR trains to be ATO driven the way tubes are

I'm not sure actually. ATO is expensive to install and as you have to programme every change of speed on every route - and this could be different for every type of train, doing it on NR would be a massive undertaking.
The principal benefits of ATO are in allowing very small headways and minimisation of variation between trains. The differences between ATO and human operation are typically on the order of seconds. On a railway like LU where you are interested in getting the absolute maximum throughput over a relatively short distance, seconds are very significant.
For the majority of the NR network headways are much long, the variability greater, inter-station distances much greater, etc, which means that the cost of ATO will far outweigh the possible benefits.
Possibly you'll see it on parts of commuter routes, but I can't think of many NR routes that would see benefit over the entire line. Perhaps LO and some of the south London inner suburban routes (and even then you'd need significant frequency increases to make it worth it), but that's about it.

Surely driverless cars would make many police officers and parking attendants redundant

You may not think it is needed but I think in the future all transport will be automated. As I said in is little is 20 years time you could find that all cars will be self-driving. There will be a time when quite simply computers will be better at doing these things than humans will.