Who is responsible for buildings insurance in a share of freehold property?

Hello, I’m hoping for some advice or a steer in the right direction. I own a first-floor flat with a BTL mortgage in a converted residential property where I have a share of freehold with the ground floor flat.

For a few years, the previous owner had an agreement where they got buildings insurance for the property. Since then, about 5 years ago, a new ground floor owner has moved in, and I’ve slightly neglected things as my wife had twins.

The new owner has taken out a buildings insurance policy, but just under her name and her flat and subsequently has made a subsidence claim which is underway.

So, I appear to be left with my flat having no buildings insurance! I don’t know if this is a responsibility issue in terms of her responsibility for the ground floor part of the lease an insurance issue where effectively she’s been missold, as she never should have been given buildings insurance for just her flat!

Do I need to get legal advice? Any thoughts to try and untangle this would be greatly appreciated.

Thanks,

Joe