Would love suggestions on where to go in London and Dublin to get the best exchange rate on the GBP and Euro....
Actually, as close as your wallet: ATM machines and credit card, Rick explains it here: Money 101
Check to see what your bank/credit card company charges for foreign transactions. Some have a 3% charge.
In travel in over 50 countries I have found that the best, easiest and cheapest way to obtain foreign currency is at the ATM. I Stay away from money changers, American Express checks, exchanges and banks.
In addition, if you can pay by credit, use the card and save the cash. You'll get the current exchange rate of the day from your card.