Yes, it certainly looks like a White Stork, Claire. I don't know whether you are aware but there's a project to reintroduce them to various sites in southern England. You can read about it HERE.
The exciting news is that a pair successfully hatched three chicks on the Knepp Estate in West Sussex - the first in the UK for 600 years. It could be that your bird has come from there.
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Tony
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