What are reasonable access rights to a shared driveway in the RH11 7TP area

I have no idea what area that is.

I believe that driveway easements are pretty much the same in all states - they are to be kept unencumbered at every single moment. No 'I just have a guest for an hour' or 'I'm entitled to the left side and you can do what you want with the right.' NOTHING can be placed on them, built on them, planted on them, and they can't be altered without mutual agreement.
But of course disputes end up in court all the time, so tell us the situation in detail.

If you have a shared driveway, the easement should be spelled out as part of the deed. Or are you asking about new construction?

I think that's a postal code in the UK, but I'll bet the definition is the same.

Is this in West Sussex UK? Laws in England are a bit different than the USA. Here is what one source has to say "•Shared driveway - without a right of way you cannot access your property. Not only will you need to ensure that there is a right of way that you can benefit from, you will need to identify whether this right provides for both vehicular and pedestrian rights of way."