Meaning of trade: Mutual trading and members clubs: mutual associations: specific activities: mutual health insurers: are they trading?
Whether particular activities are conducted in such a way as to amount to a trade is essentially a question of fact. There is detailed guidance at BIM20050 onwards. At the margin the issue can call for fine judgement.
The insurer will have been authorised under the Financial Services and Markets Act 2000 to carry on business. It seems unlikely that such business will be conducted in such a way as not to amount to a trade. But you will need to establish the facts in each case and confirm the position.