I think your latest updates change the picture quite a lot OP unfortunately.
An £8k loan and a £12k loan within the same month is not consistent with being short while you were on maternity leave. If the household genuinely just needed a buffer, why was £20,000 of borrowing required in one month? It’s a huge sum and I worry the tip of the iceberg.
You need to sit with him and his accounts and get him to spell out the paper trail for you with transactional proof: £12,000 loan lands in current account on X date. What happens to that £12,000 afterwards? Does it pay off another card? Go to Trading 212? Leave in cash transfers? Pay another lender? Disappear in smaller transactions?
I would literally work through the large loans one by one and follow the money.
The credit card statements you haven’t seen yet are also really important because a huge amount of spending could have happened directly on those cards and wouldn’t necessarily be obvious from his current account.
Trading 212 deserves proper scrutiny. It is a legitimate investment platform but using borrowed money to trade or invest while carrying substantial consumer debt is very high risk behaviour and depending on what he was doing there, the account history may explain some of the borrowing. The important thing is not just how much he deposited but whether there were repeated deposits, withdrawals, realised losses, leveraged products/CFDs.
The previous mortgage incident is defo relevant. This isn’t a first time financial mistake. He has already experienced the consequences of hidden debt and still appears to have continued concealing huge borrowing afterwards.
Before you even think about paying anything off / deciding on whether your marriage survives this I would:
Get both credit reports. I would want to see all three credit reference agencies eventually, because not every lender reports identically everywhere. That will show open accounts, balances, limits and recent credit applications.
Ask to see the path of what happened to the loans and to the £5k car insurance payout. If someone has serious debt and suddenly receives £5,000, that is an obvious opportunity to reduce it. If it went elsewhere, where?
Safeguard the mortgage if this is in your name too. If you’re both named on it you’re both liable. If for some reason he stopped contributing, the lender can still expect the full mortgage payment to be made.
Given what you’re uncovering, I would want to establish whether the mortgage is completely up to date (don’t rely on him to tell you, ask for paperwork). Exactly what account is it paid from and is the money for the next payment protected?
Are there any other joint loans/overdrafts? Are all of these mystery loans definitely unsecured? Has there ever been any further borrowing secured against the house?
Ask if your mortgage lender can put any safeguards in place so that additional borrowing against the property can’t happen without your involvement.
Protect yourself financially now. You need to know exactly what joint liabilities exist x