You must identify a lawful basis to process personal data
For all data processing activity you do under the UK General Data Protection Regulation (UK GDPR), you must identify a 'lawful basis' (or bases, as you can choose multiple) to justify the processing of the personal data.
You'll have to decide which basis to use on each occasion, based on the context and details of your processing activities.
Your processing always needs to be a ‘necessary and proportionate’ way of achieving your underlying task. You can only collect the personal data you actually need (not just data that will be useful), and must choose the least intrusive option available to you.
This is one of the 7 principles of data processing under the UK GDPR - get further details on the principles in our summary article.
You can justify processing data if the activity falls