Consent to alter withheld. What would you do?

[MH0084]

Long-story short, consent to alter was withheld by the co-freeholder. Except for one point that I did know it would sensitive but decided to ask anyway, all other changes were withheld based on "concerns on the impact of the changes in their property". Which for all I offered strong mitigation with specs many times above minimum required by building regulations.
Now I'm left with 3 choices and don't really know what to do

To what extent is the FH's refusal likely to deter a potential buyer?

I was not doing it for a potencial buyer as I was planning this to be my forever home. Refusal means I spent £25k in project fees and the place won’t work for my family as I need 3 bedrooms and the property is currently 2. Overall still a nice place. Would not be a problem to sell.
However, sellers would wonder I didn’t go ahead with the planning permission. I would not be able to lie about disputes with the neighbours. I guess if the buyer is happy with current layout would not be an issue.

I would sell, if it no longer fits your needs as is. Spending more money on new plans and specs with no guarantee they’ll alter the co-freeholder’s decision when you could instead put that money towards a move is a big risk. Buyers may query why you didn’t go ahead with extending, but many prospective buyers will be equally content with the size and layout as it is, particularly if the flat is in a desirable location.

Many people get planning permission for projects they don’t actually do. So I wouldn’t worry and just sell it

Just to update on this.
I have asked the designer to do some amends on the project and see if they approve. But if not, I have decided that I will fight in court. There’s no way I can afford a freehold property in London and honestly they are being abusive and a bit delusional about their power over my property.
Even if I get to spend few grand on solicitors, still cheaper than moving considering stamp duty, mortgage prepayment, actual moving costs and real estate agent fees.
It’s not gonna be pretty but at this stage I don’t have other option.
Perhaps when DC are older I can move but atm not possible due to co-parenting and school arrangements (my flat is 5 minutes walk to DC’s school).
Don’t understand why people want make other people’s lives miserable for no reason.