If you have a Openreach FFTP fibre modem. If you change to another FFTP broadband provider if they use the Openreach system will you need a engineer visit?
So long as you're ordering a 1Gbps or slower package, then the same ONT (optical modem) should be retained. But there are some newer 1Gbps+ plans, based on Openreach's 1.2Gbps and 1.6Gbps tiers at wholesale, that will need a new ONT installed as they require a 2.5Gbps port.