Help?? we have flooded the bank downstairs.

A question about : Help?? we have flooded the bank downstairs.

I am at my witts end, can anybody possibly offer some advice? I am literally shaking with worry.
We live in a flat above a bank. The recently bought the leasehold.
This evening we heard water and ran to the kitchen to notice that the kitchen sink had overflowed.
The kitchen was covered in water as the overflow had not coped with the water.
We have cleaned up all we possibly could, but on looking through the window of the bank downstairs, I can see that this has affected the bank greatly. There is a huge pool of water on the floor and the water is dripping through the ceiling tiles.

I am hugely concerned as to what price this will cost us. Foolishly we have not yet obtained our contents insurance.
The buildings insurance is in place for the whole building by a company who own the freehold, and who rent the space downstairs to the bank.

Will we personally have to pay for any damage caused downstairs? I dread to think what might happen if the banks insurance company need us to pay for loss to computer systems or anything like that.
Can anyone offer any advice at all?

Best answers:

• If you're worried the longer it is left the more damage it could do .....you could ring the police who will have contact details for the keyholder and get in touch with them and let them know.
• Thank you Duchy. That would have been great. Perfect Idea, however the bank have never supplied any contcat numbers for these kind of occasions. They have ours, but have never given theirs. I would have liked the opportunity to let them know right away, to minimise damage. But no-one knows their number. On the occasions their security alarm has gone off, the police have been unable to find out any numbers of keyholders also so the alarm just keeps going off all night!
  Ideally, I could have let them know right away before tings got worse. But I think all we have to do now is wait until the morning.
• As far as I am aware, any damage caused by this flood should be covered under your buildings insurance, as along as you have accidental damage cover. (Presuming you left the tap running & it wasn't an actual leak.)
  However I thnk you would need contents cover for this like carpets etc.
• I understand that Banks need more liquid funds.....
• I am sure they have something put aside for a rainy day - well done you