We're traveling to Europe in September that will include a week in London. I've read that merchants do not like to give change back for small cash purchases and that tourists should have exact change for small items. We intend to use credit cards for the most part, but for a cup of coffee or such we will be using cash. I understand the smallest denomination is the 5 GBP note. Do I need to get coins asap after we land in London? Thanks in advance for your help in this matter.