Thanks for your question - I am Sam and I am one of the UK tax experts here on Just Answer.
No not foolish at all as if you do rent out this property to generate an income, then as a UK resident you must declare this to HMRC and the only way would be via self assessment.
Your tax bill would be £3000 x 20% = £600 a year
We cannot advsie whether it would be prudent to sell the property but clearly having an income of just over £13,000 a year for as long as you let the property with the property increasing in value for each year that passes - surely is a more viable option then selling and once the money is gone its gone ? Only you can determine what your annual and short and long term needs are
But we are not financial advisers we are tax advisers which I am sure you can appreciate
Do let me know if I can assist further