Discovered 11 years later that my solicitor, developer & building control may have acted together. My flat was never signed off. What legal route now? England

My sale has just collapsed because I discovered something extremely serious: my flat was never actually signed off by Building Control, despite being sold to me 11 years ago as a completed and compliant conversion.

At the time, I used a conveyancing solicitor who completely missed this. What is now even more concerning is: • all five flats in the building were sold through the same solicitor firm • that firm also acted for the developer • Building Control issued an Initial Notice and a Final Certificate that only covered the ground floor shop, but the solicitor treated it as if the flats were also signed off • no indemnity was offered and nothing was flagged • the same solicitor firm handled both my purchase and the developer’s sale

This strongly suggests that the solicitor, developer, and the building control organisation may have been working together. I had no idea — my “date of knowledge” is literally now.

Because of this, my buyer’s solicitor refused to proceed, and my whole sale has collapsed.

I’m honestly shaken and, yes, I do want accountability. This feels like professional negligence at best, and potentially something worse.

My questions are: • Should I go straight to a professional negligence solicitor who specialises in conveyancing failures? • Do I legally have to start with the firm’s internal complaints process first? • Is the Legal Ombudsman worth using, or is it ineffective in cases like this? • Does the SRA ever actually investigate situations where a solicitor may have worked alongside a developer in a misleading way? • Is compensation realistic in a case where the solicitor missed a fundamental defect 11 years ago but I only discovered it now?

I am not looking for vague opinions — I need to understand the real legal route: negligence claim, ombudsman first, SRA complaint, or immediate private solicitor.

Any guidance on next steps would be hugely appreciated. Thank you.