The people living on the upper floor of the apartment block where I live have taken over the loft space, and have installed an electrical immersion heater. I believe the flats are leasehold; is this likely to affect our insurance?
Quite possibly. It’s unlikely that your neighbours will have a right to use this area. Your flat will probably have a management company to which you will pay a service charge. You should contact them to report a possible breach of the lease and mention your concerns as regards the insurance. It might be an idea to set up a residents committee if you don’t already have one.