Long post for clarity because I'm replying to different people and going around in a circle, plus my individual points are being taken out of context. I'm happy to be corrected but what I have been taught is...
Is it okay to block someone in?
Absolutely not. It's definitely illegal and can be criminal.
Is it illegal to block a drive?
Not by itself.
When is it illegal then?
If there is a vehicle in it as I said above. Or where there are specific bye laws prohibiting it as I and a pp discussed earlier.
What about the Highway Code?
The Highway Code is an advisory not a statute and it refers to the Highways Act 1980. It was was explained to me by my employer 15 years ago that this advisory was intended for drives and unadopted roads to public access property Eg libraries, hospitals, schools. NOT Mr & Mrs Smith at 67 Berry drive or whatever. Borough council bye laws are supposed to clarify but unfortunately people prefer to just read what suits them and stop there.
If everyone in the country dropped their kerbs nobody would be able to drive anywhere anymore. If you have a genuine reason why your property needs special access the council will paint a disabled bay, or double yellow or other road markings to lawfully prohibit parking.
Furthermore you have an issue that the council is sympathetic to but doesn't give you the right to prevent parking they will paint a single white line.
There also are areas with bye laws preventing all parking in front of all drives for example new build estates
What about morals?
This I actually agree with, parking across a drive should be a reasonable last resort. But I'm not going to walk for miles just so you can stake your claim to your little bit of Britain.
Plus I have never minded people parking across my own drive if they left a number to call. Because if I really need the drive I would call them. If I didn't need the drive I would park somewhere else.
I lived most of my life in London where parking space is often scarce. Politeness should go both ways. And I think it's rude to make everyone around you suffer so you can have your own little private oasis that you are not entitled to. Most of the people irl that have done this are usually very typical territorial bullies.