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How many people go fishing in the UK?
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you can only really have a estimate on this, quote"I read that last year over one million rod licences of all types were sold" end quote in my estimation you could safetly say theres a lot more that dont buy the rod licences a good source would be to look at Environment Agency.

Addition
Angling in the UK is often quoted as the highest participant sport

there are estimated to be in excess of 3 million anglers in the UK

You only need a fishing licence for coarse & game fish

A licence is not needed for sea fishing