UK garden birds that arrive in flocks

A sudden flock in a garden is most often starlings, long-tailed tits moving through as a group, house sparrows, or winter thrushes stripping a berry bush.

10 of the 30 birds on this site fit. Each one links to its full page, with what separates it from the ones it gets mistaken for.

Not here? Describe what you saw — the identifier ranks every garden bird rather than filtering them out, so it will not hide yours.