The immediate cause for the Act was a trio of cases in the House of Lords, which had for the first time imposed damages in tort on trade unions for going on strike.

But in Allen, the House of Lords held that a trade union could not be sued by a non-union worker for pressuring the employer into not hiring them.

Quinn v Leatham ended all possibilities of a closed shop and South Wales Miners' Federation v Glamorgan Coal Co held that a union which induced a breach of contract had no defence of an "honest motive" (for instance, wanting to improve working conditions and get fair pay for employees).

A minority in the new Cabinet, including Campbell-Bannerman and John Burns, wanted to introduce a Bill stating that trade unions could not be liable for damages.

The Private Members' Bill was severely criticised by the Attorney General for England and Wales, John Lawson Walton, "who tore it to pieces in his best forensic style".

[2] Without warning his colleagues Campbell-Bannerman spoke in favour of the trade unionists' Bill: I have never been, and I do not profess to be now, very intimately acquainted with the technicalities of the question, or with the legal points involved in it.

[2]The Conservative MP George Wyndham said he had heard Campbell-Bannerman's peroration with blank amazement as it was incredible that he should on Friday request that MPs vote for a Bill which his Attorney-General had strongly denounced on Wednesday.

[3] George Dangerfield wrote in his The Strange Death of Liberal England: It gave the Unions an astounding, indeed an unlimited immunity.

[5]The economist Joseph Schumpeter in his book Capitalism, Socialism and Democracy said of the Act: It is difficult, at the present time, to realize how this measure must have struck people who still believed in a state and in a legal system that centered in the institution of private property.

In London Underground Ltd v NUR, Millett LJ said, "a right which was first conferred by Parliament in 1906, which has been enjoyed by trade unions ever since and which is today recognised as encompassing a fundamental human right".