https://www.theregister.co.uk/2017/07/26/o2_fesses_up_to_throttling_network_abroad/
https://community.o2.co.uk/t5/Pay-Monthly-and-Pay-Go/O2-EU-Roaming-versus-Vodafone-Three-Asda-BT-and-Tesco-Dublin/td-p/1060568
British O2 contract customers only seem to be affected.
Limiting bandwith could be the loophoole for the providers to keep costs down within new roaming regulations ...