Help on the way...
I stringly suspect that, in a Civil War between Blueshirts and the government, the British would provide whatever the government needed in the way of resources to the government. They would most likely, IMVHO, try to avoid puting troops in there, because that could weaken the goverment's support among its own people. They might also provide air support, or even volenteers. For that matter, there's almost always a fair amount of Irishmen in the British army--easy enough to transfer volenteers to the Irish army.
Incidently, I'd expect it to be a very ugly civil war, with plenty of executions, judging from the previous civil war. When the dust setles, Britian probably gets its leases on Western Ireland bases reinstated--that helps a LOT with the Battle of the Atlantic.