To what extent did the powers of the government in Britain increase during the First World War?

The English government during World War One increased its power over both domestic policy and foreign policy in many ways. First and foremost, Lord Kitchener’s army had vast power to conscript soldiers from everywhere in the British Empire. Additionally, the armed forces, under the civilian command and oversight of first H. H. Asquith and then Lloyd George's government, took direct control over the British economy, turning its vast manufacturing power toward the aim of arming, clothing and feeding British soldiers. Moreover, with the knowledge of senior government officials in parliament, Downing Street and the army and navy, the civilian government set up a completely off-the-books domestic surveillance program that supplemented and at times over-rode military intelligence. This secret service, into which academics and wealthy aristocrats were drafted, was engaged in all manner of domestic and foreign spying, most of it unlawful, in the sense that neither the House of Lords nor the House of Commons had created any such service, or given oversight mechanisms to regulate what would later become MI5 and MI6.

As for freedom of press and speech, although neither of these rights are guaranteed in England even today under law, there had long existed a good deal of tolerance for those who spoke out against the government and in favor of socialism, unions and against the aristocracy. Publications that engaged in these kinds of criticisms were often stifled during the war and those deemed to be engaged in subversive activities were jailed. Strikes at mines, which had been quite common before the war, were banned during the war, because the government declared coal mining an essential service, and took indirect control of that industry. In fact, when they were strikes or even the hint of labor unrest during the war, scabs or strikebreakers, often foreigners, were brought in to work the mines. 

Perhaps the most serious and flagrant expansion of government authority came in response to the Ulster Rebellion, when British Soldiers, many of them Irish, were ordered to occupy and violently suppress the Irish Catholic uprisings that begin in 1916. The occupation of Northern Ireland by British Soldiers began during the war but lasted until the end of the 20th century, circa 1999.  Lastly, no discussion of increased British War powers could be complete without the mention of the complete whitewashing of the terrible realities that British soldiers fighting the war faced. The propaganda machine that Britain put into place heavily censored all soldier's letters home, tolerated only positive (mostly false or highly misleading and selective) news from the front, so that those back at home were for a long time under the false impression that the war was going well and that victory was assured and would come soon. Those who reported the reality of the war, especially if they were soldiers, were imprisoned and or executed, and labeled traitors. No distinction was made between telling the truth about the conditions on the front and directly spying for the Germans. This was a moral and legal outrage, but it was not unique to England. 

The gravity of the war made it possible for the British government to expand the scope of it war powers inward and to blanket the home front in a very tight, all encompassing, and not altogether benevolent embrace.