Water leak to another flat, who's responsible?

Other

We have had a small leak from our flat from a washing machine that has leaked into the flat below. I have not yet seen the damage to the flat below but there is no damage in our flat so I dont think it can be too bad. The flat is in a purpose built block, so the floors are concrete.

So my question is, who is responsible if there is damage to the downstairs ceiling, appliances etc? Is it ours as landlords, our tenants, the leaseholders, or the owners of the flat below?

We do not have contents insurance as the flat is let unfurnished, the leasholders do have insurance and I have a copy of it. It is 'buildings, contents and property owners liability insurance' for the whole block. It does say that the insurance covers flood and escape of water.

Another question, if it is the responsibility of the leaseholders there is a £250 excess on their policy, do we pay it or do the leaseholders.

Thanks for any advice.
Neale