For Many years the Building Industry in the UK had a bad reputation regarding Health & Safety, so some years ago the Government Introduced legislation to improve this situation, this Legislation has recently been updated and is called:

The Construction Design & Management Regulations 2015 (CDM2015):

Below are two short extracts from the HSE advisory leaflet, which you should read

All Clients

Most clients, particularly those who only occasionally have construction work done, are not experts in construction work. Although you are not expected to actively manage or supervise the work yourself, you have a big influence over the way the work is carried out. Whatever the size of your project, you decide which designer and contractor will carry out the work and how much money, time and resource is available. The decisions you make have an impact on the health, safety and welfare of workers and others affected by the work.

Domestic Clients

If you are having work done on your own home, or the home of a family member, and it is not in connection with a business, you will be a domestic client. The only responsibility a domestic client has under CDM 2015 is to appoint a principal designer and a principal contractor when there is more than one contractor. However, if you do not do this, (as is common practice) your duties as a domestic client are automatically transferred to the contractor or principal contractor. If you already have a relationship with your designer before the work starts, the designer can take on your duties, provided there is a written agreement between you and the designer to do so. 

The complete text of the advice can be found at the HSE website