He entered the House of Commons at the 1900 general election, relatively late in life for a front-rank politician; he was made a junior minister, Parliamentary Secretary to the Board of Trade, in 1902.

His campaigning helped turn Liberal attempts to pass the Third Home Rule Bill into a three-year struggle eventually halted by the start of World War I, with much argument over the status of the six counties in Ulster which would later become Northern Ireland, four of which were predominantly Protestant.

To supplement the family income, he bought a small farm on the Richibucto River, which Bonar helped tend along with his brothers Robert, William and John, and his sister Mary.

Her brothers Charles, Richard and William were partners in the family merchant bank Kidston & Sons, and as only one of them had married (and produced no heir) it was generally accepted that Law would inherit the firm, or at least play a role in its management when he was older.

To cover the costs of the Second Boer War, Lord Salisbury's Chancellor of the Exchequer (Michael Hicks Beach) suggested introducing import taxes or tariffs on foreign metal, flour and grain coming into Britain.

[32] After returning from a speaking tour of South Africa in 1903, Chamberlain found that the new Chancellor of the Exchequer (C. T. Ritchie) had instead abolished Hicks Beach's corn duty altogether in his budget.

[32] Angered by this, Chamberlain spoke at the Birmingham Town Hall on 15 May without the government's permission, arguing for an Empire-wide system of tariffs which would protect Imperial economies, forge the British Empire into one political entity and allow them to compete with other world powers.

[35] In parliament, Law worked exceedingly hard at pushing for tariff reform, regularly speaking in the House of Commons and defeating legendary debaters such as Winston Churchill, Charles Dilke and H. H. Asquith, former home secretary and later prime minister.

[37] His speeches at the time were known for their clarity and common sense; Sir Ian Malcolm said that he made "the involved seem intelligible", and L. S. Amery said his arguments were "like the hammering of a skilled riveter, every blow hitting the nail on the head".

[37] Despite Law's efforts to forge consensus within the Conservatives, Balfour was unable to hold the two sides of his party together, and resigned as prime minister in December 1905, allowing the Liberals to form a government.

[43] In 1909, he and his Chancellor of the Exchequer David Lloyd George introduced the People's Budget, which sought through increased direct and indirect taxes to redistribute wealth and fund social reform programmes.

[44] The Liberals called a general election for January 1910, and Law spent most of the preceding months campaigning up and down the country for other Unionist candidates and MPs, sure that his Dulwich seat was safe.

[70] In terms of social reform (legislation to improve the conditions of the poor and working classes) Law was similarly unenthusiastic, believing that the area was a Liberal one, in which they could not successfully compete.

[73] Lansdowne argued that although the electorate might prefer the Conservative Party if they dropped food duties from their tariff reform plan, it would open them to accusations of bad faith and "poltroonery".

[74] Law postponed withdrawing the tariff reform "Referendum Pledge" because of the visit of Robert Borden, the newly elected Conservative prime minister of Canada, to London planned for July 1912.

[78] Law again wrote to Strachey saying that he continued to feel this policy was the correct one, and only regretted that the issue was splitting the party at a time when unity was needed to fight the Home Rule problem.

"[79] Law met the Lancashire party on 2 January 1913 and ordered that they must replace any food tariff based resolutions with a vote of confidence in him as a leader, and that any alternative would result in his resignation.

[87] The legal scholar A. V. Dicey, himself an opponent of Home Rule, wrote in a letter to Law that the threats of violence were "the worst mistake" that undermined "the whole moral strength" of the Unionist movement.

The spectre of civil war was also raised – the Ulstermen began to form paramilitary groups such as the Ulster Volunteers, and there was a strong possibility that if it came to fighting the British Army would have to be sent in to support the underfunded and understaffed Royal Irish Constabulary.

[92] The third complaint was that the Liberals had still not honoured the preamble of the Parliament Act 1911, which promised "to substitute for the House of Lords as it at present exists a Second Chamber constituted on a popular instead of a hereditary basis".

[94] In July 1912, Asquith travelled to Dublin (the first sitting prime minister to do so in over a century) to make a speech, ridiculing Unionist demands for a referendum on the issue via an election and calling their campaign "purely destructive in its objects, anarchic and chaotic in its methods".

[102] Another Tory peer, Lord Sailsbury, wrote to Law that as much as he was opposed to Home Rule that: "I cannot support political lawlessness and I shall either disenfranchise myself or vote Liberal ... rather than encourage armed resistance in Ulster.

[105] Lord Lansdowne advised Law to be "extremely careful in our relations with Carson and his friends" and find a way of stopping F. E. Smith's "habit of expressing rather violent sentiments in the guise of messages from the Unionist party".

"[105] During the debate on the Home Rule bill, Carson submitted an amendment that would exclude the 9 counties of Ulster from the jurisdiction of the proposed Parliament that would govern from Dublin, which was defeated by the Liberal MPs.

[107] Law himself in a letter to a friend stated that the British public was "so sick of the whole Irish question" that the majority would probably agree to a compromise of a Home Rule for Ireland sans Ulster.

Law arrived on 13 September, and again pointed out to the King his belief that if the Government continued to refuse an election fought over Home Rule and instead forced it on Ulster, the Ulstermen would not accept it and any attempts to enforce it would not be obeyed by the British Army.

[119] Law's critics, including George Dangerfield, condemned his actions in assuring the Ulster Unionists of Conservative Party support in their armed resistance to Home Rule, as unconstitutional, verging on promoting a civil war.

The entire Party then left the Commons silently, and although a strong protest (Asquith later admitted that "it was unique in my or I think anybody's experience") the bill was still passed, although with a suspension for the duration of the War.

Members included Kitchener, Law, Churchill, Lloyd George and Lansdowne, with the make-up divided between political parties to defuse tension and provide criticism of policy.

[137][page needed] Besides the recent Irish Treaty and Edwin Montagu's moves towards greater self-government for India, both of which dismayed rank-and-file Conservative opinion, the government's willingness to intervene against the Bolshevik regime in Russia also seemed out of step with the new and more pacifist mood.