UK Compliant Drainage Design Project

I need a drainage design creating for 2 properties. It needs to comply fully with UK building control regulations and must satisfy the local water authority. It needs hydro modelling to demonstrate it's compliance with the regulations and advice as the the best solution for our specific site. A comprehensive knowledge of UK drainage rules is necessary. We have an indicative layout with site levels and drain invert level, the freelancer needs to either adapt and refine this or advise on an alternative scheme.