As i mentioned in a previous post im currently paying 3p a click on adwords whcih isnt much but im only promoting an item with a 1:5.5 conversion so at 3p the profit margin is a bit iffy. I have noticed that if i sign up with a new account and select to pay in $ not £ then the min bid i pay is 5c (about 2.4p) again whilst it isnt much of a saving £ wise in temrs of % saved it is a fair bit. Is there any reason that now i have signed up to pay in $ not £ Google will send me an email saying 'you are in UK not USA so your account has to be in sterling not dollars'?
Adwords is agnostic to the currency you use (at least in theory), so no, you won't receive any email / error / alert.
No, it will not be a problem your currency - but probably you won't be able to perform prepayment via bank transfer. I would send they an email asking to them transfer your campaigns to the new account (after you create and activate it) - so you will not loose your quality score history.
To build a good Quality Score (that is based on your CTR% history) it may take one month or two depending of your daily traffic. This is why AdWords staff has this procedure that they manually migrate your quality score from one account to another account.