Law on lead Gas pipes
Law on lead Gas pipes


Existing installations that are not leaking or faulty do not have to be replaced.

See Is it necessary to replace lead gas pipes?


  Should he have cut the gas off and left them vulnerable


Only if there was a gas leak or the installation was in a dangerous condition. If so I believe he should have given them a written notice. 


  He is charging them £600 to replace pipes


Get at least one (preferably more) separate quotations from different companies.

As a matter of principle I would avoid giving additional work to tradesmen who invoke the law to obtain additional money. Often tradesmen/engineers will tell you what is required for new installations as if that had to be retrospectively applied to existing installations - the law does not require that (in general) unless there is a defect or a major change. 


  they now feel cornered to have the work carried out by that company.


I would urge them to stop dealing with this company. In their position, if pestered by people from this company I would just say I am arranging for any problems with the installation to be dealt with and leave it at that. I would cut off any conversation at that point. There's absolutely no need to communicate further with a company that makes you uncomfortable, they have no rights to make any demands of you. 

If their bill for work already completed to your daughter's complete satisfaction seems unreasonable,  I would write to the company saying you dispute the bill and I would try to take the matter up with trading standards and get free advice from the citizens advice bureau. Keep written records of everything that was said and done.