Dave - yes, as (Paul/Master?) McGrath of Harlow reminds you, he hasn't murdered anyone and I'm not suggesting he's being mistreated because he's Irish and definitely not that 'the Brits' are involved. I assume most US citizens who can't afford decent legal representation (which is a good chunk of them) end up in the same sort of Kafka-esque scenario in similar circumstances. Where he's being held, I also assume the majority of his fellow detainees are of Hispanic origin also awaiting deportation. No particular propensity to piss off solely the Irish, as far as I can see.
Definitely no involvement by Her Majesties Government.
We're not trying to get him out or acquitted - that's for a US court to decide, clearly. We're just looking for means of getting around the isolation arising from his being locked up 1500 miles from his immediate family and 4500 miles away from the rest of his family (in Dublin).