You mention the new job is in the Northern part of England, where are you now? Typically lower salary implies lower taxes. Depending on your life style, and where you live 124 in down town london might actually be equal to 60 in North England.
How much does your house / apartment cost each month? Is it more expensive to own a car in one verses another.
Add into the equation, and this is the hard one, how much is it worth to you to do more meaningful work?
How much is job security worth? I expect with your upcoming changes from leaving the EU, one of your possible jobs might be more at risk.
How many hours a week will you work at each? Do you have friends in one location you would miss? Do you fly somewhere for Christmas, which might cost more or less in the other town?
Will the lower salary prevent you from retiring early? Myself I love programming so I will do it forever. So a slightly later retirement has no meaning to me.
All in all there are a lot of quantifiable numbers you need to consider. There are the intangibles, but you need to list those out. Try and put a value on them, for comparison sake. You will have risks to consider - job security. Opportunity options - vesting in a startup. Although I think, mathematically your odds are 1 out of 10.
Good luck, and count your blessing you can make a choice.