Might be a bit late here but I'm not often in this thread...
Starting a family can be an expensive business but the difference in wages between the jobs is not insurmountable with a bit of minor budgeting. I may be guilty of assuming but it doesn't sound like you're in a job hovering around the minimum wage mark on PT hours and there's plenty who manage to raise a family on less than stellar wages.
Regardless of money you can't buy more time. Less commuting, less time abroad and regular hours with flexitime all in what sounds like somewhere you'd enjoy working sounds perfect. If you and you're other half can concentrate on family life in a reasonably structured way without work being a constant problematic intrusion it's a massive help. Just both of you being available so one can look after the baby and let the other go and have a soak in the bath, nip out for a pint or just have a lie down will be worth way more than the difference in wages.
Just think of how it would feel if you knew your partner was having a hard time of it with the baby and you were stuck in India? You'd happily give 10 times that £600 just to be able to get back and help out.
I'm gonna look a right nasty bell if you've took the London job though....
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