https://www.slab.org.uk/faqs/can-i-use-data-i-get-from-a-referral-service-or-other-source/
It is important to check that your client is happy to share their equality data with us and that it remains accurate. This will also ensure you comply with data protection legislation.
You should still explain to your client why we ask for this information (see “Why we need to collect equality data” above) and then you can use the data you have been given to confirm the information is correct.
For example, when asking about Sex you could say "the [organisation who gave you the data] has told us your sex is male. Is that correct?”
It is important that your client knows that they have the option to answer ‘prefer not to say’ for all the equality questions apart from age.