It's for an electric shower, and it's a registered electrician you need (or a plumber who is Part P Electrical qualified and belongs to a competent persons scheme).
As a plumber I always work in conjunction with a mate who is an electrician. I install the pipework and mount the unit on the wall and my work stops there.
If you do an electric shower yourself and are unqualified, you won't end up in jail unless someone gets electrocuted or your work causes a fault or fire etc. If anything goes wrong any insurance cover you have will be invalid and if you come to sell the house you may run into problems.