Hmm... my EPQ revolved around some issues and interesting things that some research around the world has shown and then my application of that knowledge to the UK.
For instance, a research paper conducted in Brazil found that malnutrition (or lack of Calcium ions) can influence children developing dental fluorosis (drawback of too much fluoride intake) but when you apply that to the UK, according to the NHS less than 3% of our children are malnutrition, so it wasn't a major factor in deciding the conc of fluoride in our tap waters.
But obviously I said that in much more detail and examined the theories explaining the effect of Ca2+ ions on children's developing enamel etc.
Before you decide on your title, I would suggest you make a MASSIVE list of questions that intrigue you (and are relevant to your uni course) and then discuss on the best one with your supervisor and modify it etc.
~after you're 100% sure on the title, make a similar list of sub-questions, and discuss them thoroughly with your supervisor again
after you're happy with the questions, list them in some rough order (e.g. 1=introduction) etc. and start writing some rough drafts to get the hang of it
Sorry this is long