It is vital to avoid non-confidential disclosure of a possible invention before an appropriate patent application has been filed. This is because patent law in the UK, Europe and much of the rest of the world requires an invention to be both new and non-obvious over everything known to the public anywhere in the world (the "prior art") at the relevant date. If you make a non-confidential disclosure before filing a patent application, then that disclosure could deprive your invention of novelty and render it impossible to achieve a valid granted patent.
A patent can be invalidated by an act as simple as telling your idea to one person who is not under an obligation to keep the idea confidential. You can talk to professional advisers, such as patent attorneys and solicitors, who are by the nature of their business under an obligation of confidentiality to their clients. Otherwise, you should take professional advice and file any necessary patent applications before you make any non-confidential disclosure. As to the possibility of making a disclosure in confidence, please read our separate article on the subject: how can I use confidential disclosures? We also have a PDF summary of issues around disclosing inventions.