Should I split equity in house I own solely?

This.

You bought the house as a couple even if technically on paper. You have built a life together not just had him move in.

But I would absolutely lose my shit over the secret debt.

That is a bigger problem than 50/50 on the house.

This is how I would see it too. Did you discuss finances before having a child?

16K you
7K him
10K you (now)
He's paid >mortgage but you have facilitated his job by providing childcare.
Both of you needed for joint mortgage.
Loss of interest on car repayments and loss of interest on the 5K he will be paying you back.
You ought to have 10K ringfenced just for you then split the profit 50/50 as the original difference between you is 9K.
Add on an extra grand for interest on the 5K lump sum "lent" that is being repaid slowly and from the car pending how much that outlay was.
Mortgage payments on his part balance out you being a SAHM (are you getting pension from claiming child allowance, even if you aren't receiving it?).
Going forward, % of his salary goes into your savings account or a joint one that cannot be touched.
Unless your relationship is teetering/over, in which case you need to stay put until you can go back to work full-time then you'd need to pay him back the £2K/ the mortgage payments and give him all the furniture. If you are married though and he has proof of paying it and it was not an amicable split, I'd expect he'd fight you on it.

So without his contribution of 7 or8k how would you have paid for the fees and furniture? Would you have had to buy a cheaper house?

So you put in £16k and he put in £7k. Your contribution was approximately 2.28 x his. You used £2k for legal fees etc and £5k for furniture, leaving £16k to be shared between you as above.

To be strictly fair, that equity, whatever it is now, belongs to both of you in the proportion you put in.

You own the house solely as he had a poor credit score before. Since then he's secretly accrued debts.

Do you want to be financially linked to him? He doesn't sound very responsible.

Have you even checked if you could get a mortgage together?

If he had a poor credit score to start with and now has additional debt are you sure he will actually help you on a mortgage application? I would test this out first, it may well be a moot point.

I also wouldn't link myself to someone who had hidden debt from me.

Do you actually need a bigger house, or do you just want one? If you can cope where you are for a bit can you say you will buy somewhere together by he needs to clear the debt, save x amount of money and take steps to improve his credit score?

There really isn’t that much of a difference in your initial outlay if you consider his 5k towards furniture which I presume you used. It’s now 14 years later and he’s paying the mortgage while you work part time bringing up your child. You are splitting hairs.

We had a Deed of Trust drawn up when purchasing my current house (20 years ago now!). The circumstances were different - my DP and I had both sold properties but had released different amounts of equity - I think I had 60k and she had 120k. So the Deed stated that, in the event of a sale, we would each walk away with x percentage of the sales proceeds but that was on a scale so by the end of year 10 (it was a 15 year mortgage) we would both get 50%. I had young children at the time so it also said that in the event of a breakup I would have the right to remain in the house until the youngest was 18. If I could pay the mortgage of course!
Given the huge difference in our equity, this seemed the right thing to do at the time, and I had no issue with it at all.

How do you generally share money and what are your plans for the future re: marriage?

If you pool your money, consider this a genuinely life long partnership and intend to get married I'd be more inclined to just half the equity even though you put up more of the initial contribution. There isn't really a huge disparity in what you have both contributed including fees/furniture etc.

If you don't intend to marry and you aren't sure about the future you need to protect your assets as best you can.

You are partners rather than married fortunately for you. Split the existing equity according to contribution I.e. you get a part that wholly represents your original deposit including any increase in value, then you get half each of the rest.

He is absolutely right. He was paying the mortgage on the property for three years and he should benefit from splitting the equity minus your original contribution. His savings are irrelevant and your lager contribution can be accounted for in the next house equity split.

Others will advise better on the split, but you should also consider his parents’ £5k contribution, it was a choice to spend it on furniture but it was part of the capital sum you had available to put down as a deposit so should be taken account of in the same way.

My gut feeling is that he’s earned his share of the equity in your current house through paying the mortgage.

How you go forward I don’t know. I would have very little confidence in someone who had failed to stick to a financial plan we had agreed on, and also I would be asking why on earth I didn’t know until now.

Clearly just by asking this question you don't expect your relationship to last.

Put yourself in his position if you split. He has paid a lot of the mortgage, put together a lot of money for fees) furniture and will get nothing.

You have put in a deposit and some of the mortgage, but take everything.

If this was a man saying I want all the house the response from MN would be completely different.

Also you say you would earn the same as him if you were full time.
But you're not.
You're part time.
You can't say to a mortgage company if i worked FT it would be X because you're not full time.
You've enabled him to work full time by looking after your joint child and therefore saving on childcare. But the fact is he has paid the mortgage and any equity that has been increased he should also be entitled to.
If this was other way round MN would be up in arms about you paying someone else's mortgage when your name isn't on it. So he has taken a chance.
You either need to go your separate ways and buy on your own or share it out fairly in a way that you both agree.

You put in 12k
He put in 5k from parents plus a couple of grand so 7K to 8k
That's not a massive difference
You say you bought the car so lost out on the interest. How much are we talking?
He sounds a bit financially immature but you sound like a penny pincher and i don't think you're financially compatible. It just has the foundations for continuous arguments about money.

He’s paid half the mortgage course he gets half the equity

I thought this was going to be ive paid it all and now he wants some

Going forward set up a joint savings account for joint purchases and family expenses that you both pay into. One or two long term joint savings accounts and a "bills" account. Keep all the rest separate. I say this as someone who has maintained financial independence throughout but even we got to the stage where it got too messy and had to reconsider how we managed family finances.

In terms of the equity it sounds a fairly even split, but the ongoing management of family finances (not individual) sounds more of a challenge. That is the bit I would focus on.

Having said that you are at the stage in your lives where money is always going to be tighter, so unless his debt is huge and you have been paying a disproportionate amount in and he has been off on lots of holidays without you, I would cut him some slack. Concentrate on getting family savings together and enjoy your new home.

How sure are we that this man is financially irresponsible? He is paying more due to OP going part time so maybe this partly explains why he hasn't saved? And how much is the debt and what for? A one-off purchase now on an interest free card being paid off is different from debt for on-going stupid shit spiralling out of control imo.

I don't think the difference between what was originally paid in was all that much and it sounds like money could potentially continue to be a sticking point due to differing attitudes towards it. It doesn't seem much of a partnership really. Or at least they're just not financially compatible.

You've been together 14 years. I think YABU. You saved the money for the deposit while you were together. How much had his contribution to your living costs supported you to save? You contributed 12k to the first deposit but seem to minimise HIS parents' 5k and the 2/3k he contributed. Consider he put it 8k and you put in 12k I'd say that's pretty equal considering he pays a higher mortgage contribution. I would do everything 50:50. I'd put all wages money into a joint account, pay the bills, pay x amount into joint saving and then split the rest as fun money. You are either a team or your not a team.

YABU, the relationship will feel more like a landlord and tenant arrangement rather than a partnership.

you just believed he was saving…. Keep an eye next time.. would he transfer savings to you.

I agree with this.
I’m also wondering why he is overspending? What is he spending on?