There would appear, judging by the number of posts on this forum, that garden flooding is a frequent issue with new homes these days.
So yes, others have had garden flooding and yes, the house builders have done little or nothing about it!
See "similar threads" listed at the bottom.
(Yet another reason not to buy one!)
Under the NHBC standards require only a 3 metre area around the house to be free of standing water.
There is not a requirement for the general garden area.
Bellway, in common with most large house builders are only prepared to do the absolute minimum as required by the NHBC standards, rather than sort the whole problem out for their customer.