We had a similar situation. I learnt a lot.
A building regs certificate does not tell a buyer that the work meets building regs, or even that it met them at the time it was signed off. It tells you that the council has signed it off and will not ask you to pull it down / return to previous configuration.
The building regs, or particularly the guidance that councils and inspectors follow, include massive loopholes, like 'inspection of a significant proportion of the work', 'inspection will take place as far as reasonably possible' etc. The inspector will state that they inspected at two or three key stages in the process (when floor and roof support were visible, when final coverings in place) and that, as far as they could reasonably ascertain, things were ok - not necessarily great, they may have advised on possible improvements, but adequate.
There is no relationship in law between you and the buildings inspector. Their relationship was with the person to whom they issued the certificate. Thus you cannot claim damages against the council or inspector (many are private contractors now, with final sign-off by the council). We went all the way to the local authority ombudsman to be told this. (The council admitted it hadn't been their finest hour but no liability).
Thus, certification can help protect householders from dodgy builders. It does a very bad job of protecting dodgy DIYers, and their families, tenants etc, from themselves.
Especially so given that the builder / DIYer can avoid proper inspection by missing appointments, covering up poor supports and insulation by plastering over before inspection, not providing scaffolding or other access at the time of inspection. Yet, if they meet the most basic (in my view inadequate / inadequately enforced) requirements of the process and the inspector makes a 'reasonable effort' to inspect, a certificate will be issued.
So, there's carte blanche for dodgy DIY developers to do shockingly bad work to sell on.
Your best recourse is with your surveyor and your solicitor. They have professional indemnity insurance - so the ability to pay out if found wanting, or more likely in an out of court settlement, based on their solicitor's view of the likelihood of their being found liable if the case went to court.
If the work was done by a builder, who provided a guarantee, you should turn to them. If the previous owner did the work themselves, then however responsible you believe them to be, there is little point taking action against them (unless you feel so outraged on principle that you're willing to lose money on this), as any award against them will be difficult to enforce, via the usual civil route of endless demands, bailiffs etc and they could easily never pay you.
Your conveyancing forms should contain a question about whether any work was covered by a guarantee. If the answer was no, your solicitor should have drawn this to your attention. If you gave the solicitor a copy of your survey (not just showed and talked through, gave - we fell foul of this difference) you have some potential comeback with them.
Your best route is likely to be with your surveyor. This very much depends on whether they followed RICS guidance, what they said in their report, how it could reasonably be understood and how you responded to it. Remember they cannot survey things they cannot see e.g. insulation behind plaster. But, if there are defects visible, that you think they could have seen, which they didn't note and which should have led them to believe there could be bigger problems in unseen areas, you may have a case.
In the first instance, invite the surveyor round, show them the issues, listen carefully to what they say and take notes. If not happy, start down their complaints procedure. If no joy (and before committing to any formal process such as mediation) find a good litigation solicitor willing to act on a no win no fee basis if possible, show them your documented complaint and see if they think you have a case.
We did all this and eventually settled out of court with the surveyor's insurer. Our surveyor had mentioned one minor defect and recommended investigation of this but had put a very small estimated figure for remedial work against it. Arguably we should have investigated before purchase and doing so would have shown up bigger problems. We took his word for the minor nature of the repair instead. That failure to inspect could have scuppered our case but it didn't. There were other things he should have noted and, it turned out he wasn't following RICS guidance on the content or level of detail offered in his report. If he had, other possible issues or at least uncertainties would have been mentioned.
Good luck 