There are lots of careers related to birds – are you thinking of native birds? The RSPCA inspectors/vets do a lot with wildlife, and the BTO work specifically with birds. There also lots of volunteering opportunities with the BTO which is a great way to gain some experience! There are highly likely to be more as well I am just not sure off the top of my head, sorry!
If you want to work with birds, you can become an ornithologist (someone who studies birds). You could study bird migration, bird behaviour, bird reproduction, or anything else that you are interested in!
If this is what you are interested in, you should consider doing an undergraduate degree in zoology, ecology, or a related field.
You can also check the British Ornithologists’ Union (https://www.bou.org.uk/). They sometimes have volunteering opportunities for students who want to get some experience working with birds.