I have a leaking Bristan bathroom tap. I am guessing that it's the washer that requires replacement although I am knew to such plumbing jobs. I have managed to remove the tap from the washbasin but I do not know how to remove the top off it to get to the washer. I have tried with a flat screwdriver but it won't budge and just scratches the tap - see attached photo. Can anyone please advise me on how best to do this? I have attached below some photos of the tap.
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