Try HM Courts & Tribunals Service at https://www.gov.uk/make-money-claim fairly straight forward as a first step, you need to register and fill in some boxes, make description and timeline. Hope that helps.

Like my fellow electrician said above. This is horrible that we see this in our trade or any infact. If they cant do a good job then they shouldn't do it at all.
I've you have been given a receipt / invoice for works done, you could contact his competent scheme provider.
These will make him sit another assment and more take him off their books too.
Best have alook and see if they could help as well.

Contact the traders governing body.
Example Napit or Niciec .
You should be able to obtain all the relevant information from my builder.
Make an official complaint and they will organize a registered electrician to rectify any issues at no cost to yourselfs.

Well in this industry you will get cowboys.... But the only way your get your money back , am afraid it will have to be through the courts....and even then you still might not get it back or a fraction of it.

Try ringing trading standards and see what they advise.

Well good luck .
Frank