Take photo's of standing water etc, get a statement from the landscaper you
have spoken to then have a word with the solicitor that handled the sale for
you.
If the builder/developer laid the turf then you have a much better case.
If you laid it on badly prepared ground then it could be argued that you
accepted the state of the ground as being satisfactory.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk