Some other considerations:
Getting paid 25% more for contracting isn't really in your favour.
Firstly, take into account paid holidays and bank holidays, which for people in the highly skilled category is usually 25 + 8 days = 33 days (may be less, but not less than 28 days total). That makes up a difference of 13% on average.
Then there's the NI contributions - as a contractor, out of your rate you have to pay both your own and the employer contribution (double contribution). That's about another 10 or 11%. Making it 24%??? Really rough calculations....
So given that 25% more as a contractor is really just the same, is it worth the uncertainty of continued employment, the bother to have to take unpaid holidays and save up for it, the fact that when it comes to cutting staff, contractors are first to go etc etc - is it worth it? Also consider that some companies won't touch you if you have contracting experience (not now, but going forward). I know so many people trying to get out of it...
But, you then add that it's in London and yes, it's easier finding something else and something for your wife. So you have some thinking to do.
Another point to consider is that effectively you would be earning the same, but cost of living is cheaper in Edinburgh.
I have not done contracting before, but have been warned about it during my recent job search. So I'm not an expert in that field at all and I know many contractors out there will disagree with me.
Perfect world situation: permanent role in London.