I'm pretty sure condenser boilers are more efficient (94% for a new one). The radiators are on a separate loop not combined with the hot water system so you don't need human consumption rating.

Most modern houses in the UK use a "combi" boiler. That's a radiator loop heater and tankless hot water system in one. It heats the cold water feed direct for hot water on demand but that does mean a supply limit. Advantages are no efficiency loss through hot water storage, no space loss for the water tank, no legionnaires or similar concerns.

The other common type is a tanked system. Again the boiler does all the heating but in this case either feeding a hot water tank or the radiators. Hot water tanks are more common in older properties, those with pressure issues or those with too high demand for a direct feed.

We will probably be going back to tanks as we are slowly moving towards heat pumps from gas boilers.