Do I need a designated representative in the EU as a British manufacturer?

In most cases, yes. Since the UK is no longer an EU member state, British manufacturers are legally treated as economic operators from a third country. For many product categories, both the relevant EU product regulation and the new General Product Safety Regulation (GPSR) require that you designate a person resident in the EU who is reachable for regulatory inquiries, assumes certain obligations under Article 16 of the regulation and serves as a contact point for market surveillance authorities if needed. Without this person, research indicates you risk penalties of up to €50,000, regardless of whether the product itself is technically sound.