Can you confirm what your annual pre-tax income is please. If you look at the certificate, it will tell you the number of "relevant years". Can you tell me what that figure is please.
As you are a basic rate taxpayer and the chargeable event gain is treated as having suffered basic rate tax already, you have no further tax to pay at all. HMRC will have been advised of the gain but will see that there is no tax to pay when they match it to your tax file. You need do nothing other than to keep the certificate in a safe place for six years. Take a look at HS320 for information on tax and UK chargeable event gains.
I hope this helps but let me know if you have any further questions.
Your respones were fine.
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