This is a long-running issue and there's not enough hard evidence as to what the problems would be. In a nutshell, anecdotal evidence tells us that E10 can destroy rubber and fibreglass, which can obviously have a detrimental impact on older cars where these components are used. E10 is also 'less powerful' so expect to have to fine-tune your performance. There are a couple of options out there if you're concerned, involving fuel additives that might be worth looking into. Last year, the Government introduced better labelling on fuel pumps so you'll be able to see which fuel is E5 and E10.