IANAA.
My understanding is the sums are 14000 - 6000 = 8000 taxable gain.
0 taxable other income + 8000 = 8000, which is below the PA so no income tax to pay.
https://www.gov.uk/capital-gains-tax/rates has a worked example.
I think you do need to submit a SA, see
https://www.gov.uk/check-if-you-need-tax-return. The "Did you get more than £10,000 from dividends or savings and investments?" seems to be the trigger for a 'yes' answer.