As far as I can see @MikeLawrence the free SIM's are distributed through charities. There is further information with a list of charities here: Charities supporting refugees arriving in the UK
Vodafone are also offering free calls to Ukraine, but that is going to mean having to get a PAYG or contract SIM, if this is an option please see here: Support for our customers affected by the events in Ukraine
Hope the above helps your refugees.
