As you are a higher rate taxpayer, and want to save for retirement (am I interpreting that correctly?) - I'd fill up both you & partner's ISA's £40k from next year, then your pension - you can pay up to £40k in. Any extra could go into a taxable account, in low cost trackers.
Or you could go for a bigger/better area property, increasing your monthly costs - the main benefit in property as a main residence is the capital gains tax exemption when you sell. From your salaries/current mortgage it looks like you could borrow another £150k-£230k ish, but this would tie you both to your jobs, as you'd struggle to cover a larger mortgage on one income, especially your partners.
So I suppose the question you are thinking of is, would the property appreciate more than the stock market? London property has outperformed the FTSE lately, but with brexit etc will it continue to do so?
I'd tend towards not buying, unless you get a fixer upper at a great price.