Hi

Thanks for your replies.

Do you mean it leaks all the time - not just when it is flushed?

Yes, it leaks all the time.

Does it leak more when it is flushed?

Can't tell as yet.

Has the OP looked at the bolts that come through the base of the
cistern? *Are these done up tightly before installing the cistern ...

On my cistern the bolts do not go through the cistern. From top down I
have:

Flush device
Rubber washer
Cistern bottom
Mounting plate (with slots for bolts)
Plastic back nut
Doughnut
Toilet.

Still leaking...

David