Thanks for the advice. I haven't measured the wall but I would guess about 12 feet in the centre? There are no cracks at all and the base has lots of drainage holes. We've been told by neighbours that a builder with a really good reputation renovated the house for his mother so I'm assuming he did it well. It's been there for at least ten years as isn't showing any signs of stress that I can see (but I have only googled what to look for!). No cracks, signs of water leaking anywhere or bulging etc. It is on the deeds as being our boundary wall if we purchase. We did ask the agent about it and he didn't say he had any information on it. I agree joe90, wouldn't buy without an in-depth structural survey.