There is unfortunately no further description of the electronic tags in the article. But there is another article on Washington Post from more than a year ago:

Britain will electronically tag some asylum seekers with GPS devices (Published June 18, 2022)

Under the monitoring trial, people fitted with the location-tracking device will be required to report regularly and in person to immigration centers or police stations.

https://www.washingtonpost.com/world/2022/06/18/britain-electronic-tagging-migrants-asylum-seekers/

Back then it was a trial and now it seems to get a more widespread support. And it's not even for identification but a 24/7 GPS tracking device? Adding electronic tracking devices to migrants makes them join ranks with convicted criminals with corresponding court order.