Just to follow up on this. I sent the defective Neato back to Amazon
and they handled the return fantastically - they sent out the replacement next day delivery before receiving the defective Neato.
The new Neato is working well. The battery lasts lots longer (45mins ish - maybe close to one hour). I'm still a little wary that it'll fail, but that's mostly because of my previous bad experience.
However, I still think that Neato UK customer service is rubbish. It took chasing up and posts on this board to get a response, and then all they could advise was to return it to the company I bought it from. All it needed was a new battery in my opinion! Also, Neato US customer support never bothered to respond.