Money should never be your main motivator for taking or rejecting any job. I am at ACN now and despite some job offers with a higher salary, so far I've not yet been able to match what ACN offers me in terms of opportunity.
One thing I can say is that which location is more suitable for you depends on what line of consulting you are joining. The obvious example is Financial Services. It's quite clear that all of the excitement will be around London as all large FS companies mostly have their HQs in London, so all great work with large clients will be happening there rather than in Manchester, for example.
There are other things to take into consideration. One example is the total package on offer. Does EY offer you greater flexibility, better pension, better bonuses etc?
Or does the role itself seem to have more meat around it than what is offered by ACN? I can tell you one thing for sure: either or both companies can have BS roles that sound great on paper but have no substance behind them in reality.
So as you can see there is a lot to consider besides salary here. The other thing to consider about London is the cost of living there or commuting. Have you looked at the prices of train tickets lately? Given the fact that you are considering roles in Manchester and in London, I am guessing you are somewhere midway, so your salary differential can be easily eaten up by the cost of commuting unless you are prepared to live in London in which case you can easily end up worse off with your 70K+.
I know it sounds like stating the obvious but I would seriously rethink the approach to job offers to something other than just salary.