Marvellous. Then over the years the criteria changes and some bright spark says we should move again. Furthermore, who decides who decides? Is it going to be a cross party committee of MPs and members of the house of Lords? Would it be economists, business leaders, architects etc etc.
It's also not the case of just staying put because that's how it's been for years. The whole of government infrastructure is pretty much established in London, ministries, legislature. There are loads of reasons why it should remain in London. Seems the only reason some think it should go up north is because of the envy of the north over the south. In the short term there might be some cost savings but I'm not sure the Mancunians (and let's be honest that is the only other city really being considered) wouldn't be too happy when they can't afford to buy homes in the own city which is now blighted by additional airports etc etc.
And that is part of the problem. Whole ministries need to be moved out of London. A small London (or wherever Parliament is) office for the Minister - staff of 20 or 30 max, including cleaners, etc. All else can bee carried on electronically on a day to day basis. Occasionally the minister might have to travel for a particularly important meeting - so be it.