Where you are is of no issue. What you must do is look for unique selling points. Anglian will gurantee windows including sealed units for 15 years whereas Everest will give you a lifetime guarantee. Notice the word 'guarantee' - not 'warranty'. Everest, Anglian and other GGF members do not need...
Is that what you paid for last time?
You don't need scaffolding. Your windows can be fully fitted from the inside. Remember sealed units are fitted from the inside so the frame can be fitted and sealed from inside before the sealed units are fitted. What happens if your 8 or 20 floors up?
Your sealed units are blown so you will need to replace them all. At anything up to £300 each its going to cost you more than replacing the whole windows. You will be able to get cheaper sealed units but unless they are guaranteed by a GGF (Glass & Glazing Federation) member they are likely to...