OK first thing is the doors and windows can be adjusted to close tighter using the cams on the multi locking points.
If you have an Allen key you could probably have a go at this yourself.
Bovis Homes have one of the worst reputations for build quality and customer care of plc housebuilders.
Considering all the adverse information online from 2015 I am surprised anyone buys a Bovis new home.
That said, all new home buyers are wise to have their new homes professionally snagged and inspected before they legally complete. Some of these firms also offer thermal imaging surveys etc.
You now need an air leakage test and a thermal survey to get proof to show Bovis where the heat is leaking out/cold air is getting in. Not every new home gets an air tightness test and even those that do are often fiddled on the day to pass!
http://www.new-home-blog.co.uk/house-builders-are-cheating-new-home-air-leakage-testingI can recommend Paul Buckingham at
https://www.sustainablelifestyles.co.uk/ for the independent testing.
Regarding outside noise, perhaps window and door adjustment may help this too.
Mould in the en-suite is due to cold spots and high humidity causing condensation. It sounds like you have passive ventilation extractors with increased extraction when the light is turned on. In this case, the humidity must be very high and the cold spots quite cold. Be sure to open a window also for a few minutes for ventilation. Hot moist air out, cold dry air in.
If Bovis need to do any remedial work, you will discover why they have a bad reputation!