You can request that they sign an NDA, though you don’t have to do so. You might find that some co-founders are unwilling to sign an NDA until you’ve met and had at least a preliminary discussion. Whether or not you use an NDA, it’s important to carry out some simple online research to see if the person you plan to meet has the online presence you’d expect. It’s also important to mention that when you decide to work with a co-founder, your idea is simply the starting point. Any time you’re thinking about how to find a business partner in the UK or elsewhere, remember that how you work together to make it happen is what will make your business.