Well I just put a very similar answer on this thread:-
http://www.talk.electricianforum.co.uk/showthread.php?t=4338&page=2
But its applicable here so I shall post (slightly modified version):|Blushing
I would very much like to be proved wrong on this one but..
I don't think any legal action can be taken without a formal complaint from the person who has had the work done for them.
So if the customer don't want to kick up a stink cuz it was a friend of a friend who did the job and they are happy with the price and if they do complain it will tarnish their friendship with the person who passed the name of cowboy spark onto them!!!
So if the customer is happy OR even if customer may be unhappy..
but don't want to rock the friendship boat then there's naff all you can do about it.
Unless it directly affects you, you cannot complain about the quality of work that any trader has done at any other home or business!
Because IF the home owner/landlord/business is unwilling to open the door to let any investigating party in, you get nowhere!
I believe the initial point for complaints would either be to a Scheme provider,
(if it is one of their members who has been negligent) or Trading standards.
But again without a formal investigative report by some independent third party, it is just hearsay evidence and your word against theirs.
Also legally I believe the original person should be given opportunity to put the work right
Which is why... the original customer has to be involved..
Otherwise the cowboy Joe spark could in his defence quite legitimately say..
"but I hadn't finished & the customer wouldn't let me back on site!"
to prove otherwise in a court of law will be tricky without the consent & help of the customer!