If I was the seller I would not agree to its being MoTd again. Even if I had nothing to hide MoTs are a gamble. If the current MoT is good but the new ones comes up with a fail or some advisories the seller has a car that’s now less saleable.

This might be an advantage to the buyer if they can chisel at the price but why would I, as the seller, take the risk. There is a small upside for the seller if the car sails through but a 12 month MoT is little better than an 8 month one when selling.

As has been suggested an independent inspection might be the way to go. That’s not recorded against the car like an MoT and will cover more than an MoT does.

Fifty quid is not much in the price of a car, but although it may give you peace of mind, I don't think a more recent Pass will tell you much more than the previous one. As you are buying privately you should be able to learn more about the car from the seller (free) than from a new MoT - besides which a different tester might fail it :-))

I once worked with a strange rather paranoid person who used to have his Renault 5 tested every 6 months. Some other countries believe that every two years is often enough. I would just stick with the annual schedule the car is on. Are there any advisories ?

No advisories from all previous MOTs and also full service history. Maybe I'm falling into that strange rather paranoid person category:)