@EllaSW My husband works for a retail bank as a relationship manager in SW London and this is a very common scenario he sees. 2 high earners, mid 30s, looking to purchase a standard 4bed terrace in a gentrified area in the region of £1.2 to £1.5m. The mortgages are often £800k+ in these type of scenarios. It is extremely common.
The only thing I would add is age is a key factor as is whether kids will be arriving soon. He often sees that those who made that move mid 30s, very quickly had kids and very quickly had to reevaluate their finances. This often resulted in a move to Surrey 4+ years later for a slightly cheaper property and more space.
Those who made that move early 30s tended to have a few more child free years were they were able to save, grow their salaries and pay down the mortgage, which had a big impact on their ability to afford a financially less stressful life once kids did arrive.
If you don't mind me asking, how old are you and DP? And are kids in the pipeline soon?
Another thing to consider is that if you are dead set on wanting this type of house with that size mortgage as a proportion to your earnings, I would recommend doing this before children rather than after (as it may not be possible to pass affordability checks, even though you could probably still afford it).