The client should have obtained planning permission for the house construction from your local authority's planning department. This permission normally includes a clause stating the allowed working hours (eg 8am to 6pm Mon to Fri, 8 am to 1pm Sat, no working on Sundays or Bank Holidays).
Contact your local authority's planning department tomorrow morning (or email them today) to enquire what hours were permitted for this development. You could also ask the contractors today what they are doing working on a Sunday morning, it doesn't sound right to me.