Yes you should be worried - this looks like potentially serious structural cracking.
If Bellway Homes are trying to pass this off as normal, make a claim to the NHBC under your warranty.
In addition there should be no flooding within 3 metres of your actual house.
this is an NHBC warranty standards requirement. Bellway must address this too.
Quite how Bellway got to be rated 5 stars I don't know!
(Well actually I can guess, and it has nothing to do with buyers' satisfaction.)