Always deploy from source control
You MUST ensure all deployments originate from source control to maintain traceability. Use Git tags or branches to track and manage deployments.
You MUST NOT manually copy changes between environments.
Practical tips
WPRS -- Prioritisation incident
In 2016, a clinical incident review (ref. 58337) found a missing table alias in a SQL Select statement as the root cause of certain referrals which had been missed for assessment.
It found that had the code been deployed from source control, the risk of not spotting the error before going live would have reduced.