"If we could create a mass antiwar movement here to actually influence British policy e.g. mass demonstrations linked to strikes and occupations which helped either bring the government down or get them to withdraw troops to avert such a possibility then this would both help defeat the British government and strengthen the working class here."
I don't disagree. But why insist on defining this in terms of victory and defeat in the military conflict? Of course, we fight our government. If they'd been forced to withdraw the fleet, most probably it would have brought them down, or at least provoked a major crisis. But *that* is our focus - opposition to the government and its policy, rather than 'a military defeat for Britain is the lesser evil' (compared to a military defeat for Argentina).