If you want to seek protection outside the UK, yes, you should keep the design confidential until an application has been filed.
In the UK (and also the EU and US) it is still possible to obtain valid design protection after you have disclosed your design non-confidentially, provided that an application for protection is made within 12 months of first disclosing the design. However, the sooner an application is filed the better, and it is best to keep everything confidential until a first application to register the design has been made.
Wilson Gunn can advise on all aspects of intellectual property protection. Please get in touch to speak to a member of our team about design protection.