Intend eventually fly by PPL owner.
What does this mean? Do you not have a license yet, or do you intend to hire (or use) a PPL pilot to fly you around?
A PA46 is not a 6-seater if you want any range but would be OK for the UK and short hops to Europe. Otherwise it is a 2-seater.
£300k is a decent budget. You can trade between something new (not much around that's a 6-seater though) and something old but pretty capable.