Not sure about today's economics in the UK for buying over renting to learn, but i was faced with the same dilemma back in the early 90,s in LA when I was about to start training for my PPL, so i begged borrowed and stole and scraped together about 22,000 USD and bought a clean and tidy 1976 150hp piper warrior , both my brothers and my then wife and myself got our PPL out of it I then leased it back to the flight school for several years and actually netted out getting all the purchase price back and when my work was really slow i lived of the rental for a year or so. Granted I had to pull a few tricks like letting some of the FI's fly it for just the gas money on the odd occasion for private flights and in return they steered a lot of renters and students to it which kept the rental hours and income up.
Again, not sure how things would work today but in my case the numbers made sense and i did well with it.