It's really crap, if it's like north Hampshire. Every department has its own booking system and login usernames. Everything looks the same, because it's all on NHS-headed paper/webpage, but there are no links across the different systems. If you have comorbidites, which a fairly high percentage of patients will, there is just no coordination, and some health issues will affect others.
It's also inefficient. You can't coordinate to have cardiac in the morning and gynae in the afternoon. Things would need to be spaced because of the risk of over-running, but still, something could be better. You get total clashes as you have, or you have to be at the hospital on several different days - which might be better for some people, if they are going through tiring procedures. A lot of people also need to coordinate with transport and carers.
I'm IT and bureaucracy-literate, but I've been confused by cancellation letters which don't actually state which clinic they're for - I had to work it out by checking what I was expecting, but they coukd have stated it on the communication.
If someone isn't very literate, doesn't have English as their first language, finds planning and thinking abilities are impaired because of pain or the side effects medication - they don't stand much chance, and it's not a surprise the NHS has so many no shows. It must be really annoying for staff, too.
We all have individual NHS numbers. IT systems shpukd use this to link across different departments so that existing appointments could be seem for that patient, even if it didn't show you for what - like at work, if I'm arranging a meeting, the scheduling assistant shows when others have time blocked, but doesn't show for what. It woukd only show health appointments, not that you're on holiday or whatever, but at least it should avoid everything at the same time.
But NHS IT isn't something anyone wants to properly invest in (or anything else in the NHS.)