If this solicitor is working for your daughter, then part of his job is to advise and explain the legal side of things.
So if he is doing his job properly, then he should be saying "there is no building regs certificate, but that was 52 years ago so is well outside of any enforcement action, and no court will ever grant an injunction, and all action is statute barred".
If the solicitor does not say this or thereabouts, then ask him what action the Building Act 1984 will permit after 52 years, and if he can't answer, then he's not doing his job, so tell him that, give him chance to modify his advice, and if not sack him, and don't pay him.