Building regs query

JAYJAY33_2

Can anyone advise please...we have an offer for a three bed house accepted and got surveyor to check house as it's steel framed. Survey picked up that the garage conversion which is advertised as the third bedroom is only one brick deep so unlikely to comply with building regs. House was advertised at 225k, we had offer of 198k accepted after it had been on market 2-3 months. I've spoken to estate agent who is saying sellers bought house like that and they are likely unable to get retrospective building reg certificate as they are in Australia for months and they don't feel they need to drop price as they accepted a lower offer already. solicitor has advised if building regs are not secure rated it can only be sold as two bed plus storage room and so they would need to notify mortgage company. Sellers are saying they have already reduced price once so won't reduce price further to cover any work however the mortgage company valued it at the price we offered. Any suggestions here please? We are waiting on local search to come back but that could be another month yet. Unsure whether to get a builder out to price up cost of sorting the issue out but installing insulation means we lose 6inches off each wall in an already very narrow room which means we will likely need to get further extension in future. Houses sell ridiculously quickly and so this is likely out only option to buy a house as our rental tenancy is almost up so really need to make this work but unsure what to do. Sellers are saying another house advertised as two bed sold for 210k recently by them and so they feel they have reduced it enough yet a house in same street sold for offers over 170k aswell as a two bed with garage in feb, our one is slightly better condition and garage is attached where's other one was detached garage. Any ideas please? Thank you