Any of the big insurers would be fine, axa, aviva, more than, direct line etc
Be careful if you need tenants as opposed to owners its slightly different.
Or you can use a broker such as swintons as mentioned above. Hopefully you understand the difference of broker compared to insurer. With a broker you need to be careful they dont just give you a policy with a smaller insurer, unless that insurer is a specialist. (some will specialise in say students or leasees etc)
If your loaded then you can get better insurance eg Hiscox but it comes at a price.