The Charity Commission’s guidance states that all charities, regardless of their size, need financial controls (it’s part of CC8 and you can read it at https://www.gov.uk/government/publications/internal-financial-controls-for-charities-cc8/internal-financial-controls-for-charities).
If you don’t have a policy for this, then you might find what you need at simply-docs.co.uk. Just search for ‘Financial Controls Policy for a Charity’ and you should see it in the newsletter results.