to want to pay off the mortgage instead?

If you're sensible with money, you could pay off the half of remaining mortgage, this would reduce the amount you are repaying to the bank (sorry forgot the terminology, but you gt ny drift). Perhaps explain to your parents that you and daughter will have more money left over that way.

pay off the mortgage.
My kids both graduated with first class honours degrees from Russell Group uni's- they didnt have a private education

It sounds like your parents are a bit controlling, OP. Maybe have a look at the stately homes threads? Research FOG (fear, obligation, guilt).

Your desire to create a stable home environment for your child is no bad thing.

That's if you are in a fixed-rate deal. Once you are out of that you can pay off as much as you like.

I’d check with your mortgage provided that you can pay off that much in a lump sum, Mine will only let you pay off 10% in a year in a lump sum.

I wouldn't put my child in private school even if I could afford it. So it's really a question if you want that for your daughter? It's not straight forward that a private education is better than a state one, in terms of grades or becoming a well rounded person. I do think your parents are being controlled and patronising implying you aren't doing what's best for your child.

Don't you just love a gift given with one hand and taken back with another.
Do what you want to do op pay off mortgage and get a great tutor? Any extra curricular sport / activities she wants

Private school just for secondary is a lot more than £100k. So they are forcing you to stump up the difference. Which is quite different from having half the mortgage paid!

I paid for private school from aged 11yrs onwards for two children. Worth every penny, but a real grind. It’s not something to be entered lightly. Even with your parents gift, you’d be finding an additional £10k a year yourself with the way things look right now.

I think you need to have a chat with your parents about how realistic this all is. Being mortgage free or at least having a manageable mortgage will benefit you in many ways and allow you to support your DD financially more easily when it comes to extras and uni.

I would send her to state school until either end of key stage one or two, then think about private. Gives you time to save up. If you pay off mortgage you could use the money you save each month as your school fees fund. But I'm not sure how much that would be. Or split it. Keep enough for say first two years of private school as a cushion, use the rest to reduce mortgage balance.

Was the money intended for you or your child?

Can you use it to post off mortgage, then put £10k a year into savings from now?
So by the time dd is 11 you should have saved up a good chunk ready for secondary school fees

I hate when a "gift" turns out to be very much with strings attached.

Its entirely up to you how you spend the money. But a lower monthly mortgage could still benefit your child in terms of affording extra opportunities, clubs, music lessons etc.

Also, although it's a lot of money, that would disappear FAST in private school education. Plus what if you have more kids? Could you then afford another set of fees without another 100K?

I'd pay the school fees

Ha! Your parents want to gift your DC something but only pay for a fraction of it and spend your income on the rest while calling it a gift to you

They should have paid the fees directly they could have got a tax break

Ohhh! Right I see, that makes more sense, I thought they must be a bit insane.

Pay off the mortgage. The state schools will be fine. You’ll be mortgage free in ten years or so and that’s great.

That's absurd, you can't pay in advance for a secondary school she hasn't even applied for yet. Most private schools have extremely competitive entry requirements.

I would 100% have used it to pay the mortgage down, especially considering the interest you will be saving over that time.
If your DD is just about to start primary then you have 7 years to save what you would have been paying for future private school fees if you choose to, but also can open up many other opportunities for your DD - holidays, trips, extra curricular activities etc which will also benefit her massively.

Bit weird of them. Why didn't they keep the money and offer to pay fees out ofnit if that's what they wanted rather than just giving you it

It’s great to have the financial means to have the choice though. I wanted my DC to be at state schools but they had such a miserable time that their lives were totally changed by switching to private. It’s so dependent on your child, their individual needs, the surrounding schools etc, but to have the ability to change if things aren’t working out is so valuable.

If your parents wanted to pay for your dc's education, then they should have offered that - and you could have had conversations with them about what if you had a 2nd child in 5 years time, and about where the money was coming from for the rest of the cost, above £100K - and then you could have chosen to accept or not.
However, they didn't. They gave you the money and said it is up to you. They have no right to express disappointment in you making a different choice from the one they made.
I 100% would have gone for securing my own home / paying down the mortgage over paying for private school.
With lower (and then no) mortgage, you will be in a position to support her with paying for things like music lessons, and maybe if she needs some tutoring in a weaker subject at GCSE time.