From Jim's link,
"Once war was declared on 4 August, Scott however swung the Guardian firmly behind the decision, declaring in the next day's paper: "We ourselves have contended for the neutrality of England to the utmost of our power and with a deep conviction that we were doing our patriotic duty … Some time the responsibility for one of the greatest errors in our history will have to be fixed, but that time is not now. Now there is nothing for Englishmen to do but to stand together and help by every means in their power to the attainment of our common object – an early and decisive victory over Germany."

it in no way represented Left opinion
All through 1914 Britain had been riven by industrial disputes, strikes and civil unrest.
That all came to an end when the ultimatum was refused and the Left, like everyone else, put there efforts and support into the war.