To my eyes, the key sentence in OP is ' I get no fulfilment from [my job].'
If you don't enjoy what you do for a living (or get satisfaction from doing something useful even if you don't enjoy it), and you have a chance to live in a way that doesn't involve you doing that job, I'd say take the chance. That's a general rule, if you like.
OK, now fill in your own particular circumstances.
Does it make a relevant difference that you'd be moving out of London? Probably not. Much as life in London is a bit special (I'm one of those who pines for the easy availability of galleries, museums, theatres and concerts etc.), nevertheless this kind of specialness is probably not be the be-all and end-all for life with young DCs.
Does it make a relevant difference that you'd be becoming a SAHM? Probably not. Looking after your own DCs has a lot going for it. It can be boring and tedious, and there'll certainly be times you'll wish you were out doing serious things with grown-ups rather than cleaning up shit and singing nursery rhymes; but there are also lots of compensations. As for the gender-stereotyping issue wrt to DCs, yes it's an issue, but need not be decisive; after all, it probably won't be for ever. Which is a response in itself to the SAHM thing -- believe me, those few years when your DCs are with you all day every day soon pass, albeit that they'll drag on at the time, and (especially given what your current high-flying work status says about you) you'll very likely find something appropriate to do when DCs are in school and after. What you get to do then is in the lap of the gods, of course, but it's far from impossible that you'll find something that others can point to as a part of your role-model status as a working mother to your DCs (modesty forbidding you yourself from commenting thus, of course). The same goes for DP, too; he may well find something to do that involves a smaller commute, whatever. Things happen, and not always for the worse.
Yes your DP is a problem. But he has a lot invested in all this too. It is indeed a sadness to miss so much of children growing up because of time spent commuting, but on the other hand his commute may well be worth the other advantages -- to you and directly and indirectly, to your DCs. Think about all that, discuss with him; only the two of you can work that part out, knowing yourselves and each other.
Overall, it does look to me that the 'general principle' I mentioned above should probably be the deciding factor. Your DP should probably agree. Looking at things from the other end, so to speak (children grown up and left, living their own lives), both I and DP think back to similar decisions we made during our lives as parents and are so glad we each pursued jobs and careers that suited us, even with breaks, and even when this meant that some 'high-flying' aspects had to fall by the wayside. Happy, fulfilled parents => good chance for happy, fulfilled children.
Hth. Good luck.