What happens if a UK government removes benefits from EU citizens in breach of the withdrawal agreement?

Professor Steve Peers, Law School, Royal Holloway University of London Photo credit: Martin Robson, via Wikimedia Commons Recently the Reform Party proposed that in government it would withdraw benefits from all non-UK citizens, including from those EU citizens who had moved to the UK before the end of 2020. It acknowledged that this would breach the Brexit withdrawal agreement (for an annotated text of the rules on EU and UK citizens’ rights under the agreement, see here, particularly Article 15). Legally the EU response if the UK breached the withdrawal agreement on this issue (I’m assuming the Reform government would amend UK legislation as needed, to ensure that the breach was valid as domestic law) would be to challenge it in the arbitration process which the withdrawal agreement set up. (For an annotated text of the dispute settlement rules, see here). A dispute can be settled politically; if not settled, it goes to arbitration. An arbitration decision is binding, so if a party…