Watch the bird
All birds in the UK are fully protected by law (Wildlife and Countryside Act 1981 - WCA) from intentional harm. Under the same act, any active nest, including nest building or a nest with eggs or chicks in, is also protected from intentional destruction or removal and you cannot block access to any active nest. So, if you see a bird carrying nesting material or food into an area, this indicates that there is an active nest there.There is no law in the UK preventing any one from felling trees or pruning hedges at any time of year.
Regardless of the time of year, if you find an active nest you need to leave the tree or hedge until the fledglings have left the nest, then you can carry out the work.
With our warm and wetter springs and summers, hedges can quickly become unmanageable. It’s OK to use secateurs or sheers to keep a hedge under control, and if you do disturb an adult from their nest, they should return when you leave the area. Birds have different strategies for raising their young; some only nest once a year and others have multiple broods. On the whole, they tend to build new nests in different locations, but some birds, for example House Sparrows, will use the same nest all year, but the WCA still applies while the birds are actively nesting at any time of year.
Most gardeners are aware of the wildlife in their gardens, and have a good idea where and when there are birds nesting. Carry out a visual check if you can, and if necessary just leave the work until the fledglings have left the nest, then you can do the work you need to.If you are aware of an active nest and you see someone about to do some work, let them know so they can avoid that area, as they may be unaware of the nest. If they are felling a tree, again let them know so they can come back when the fledglings have left the nest and fell the tree. As all species of bird are protected by the WCA, if they continue and destroy the nest they have committed a criminal offence, which is a police matter.