But from 1890, it began to face determined resistance from shipowners, who formed an association, the Shipping Federation, to co-ordinate their strike-breaking and anti-union activity.

Nonetheless, the strike greatly increased both the funds and the membership of the union, allowing it to emerge once again as a significant force.

In 1911/1912 the growth of the NSFU was checked by a breakaway movement in Southampton and Glasgow which led to the formation of the rival British Seafarers' Union.

Yet from its inception the union expressed a belief in the possibility of industrial harmony, and announced itself in favour of establishing conciliation procedures.

In 1917 the Union provoked controversy by refusing to convey Arthur Henderson and Ramsay MacDonald to a conference of socialist parties in Stockholm, which had been convened in the wake of the Russian Revolution to discuss the possibility of a peace policy.

Other sections of the trade union and labour movement were also strongly critical of the NSFU's detrimental collusion with employers.

Criticism of the NSFU became increasingly widespread with its apparent role in the 1925 Special Restriction (Coloured Alien Seamen) Order, which is seen as the first path-breaking attempt to expel non-British-born people;[4] its failure to observe the general strike in 1926; and its support of a "non-political" Miners' Union in Nottinghamshire.

However, after the death of Havelock Wilson in 1929, the NUS quickly began to pursue a more mainstream policy and became reconciled with the rest of the trade union movement.

His connections with many antiracist initiatives including the Colonial Seamen's Organisation and the Pan-African Movement widened the SMM's links and brought international attention to the NUS's failure to back the largest black and minority ethnic workforce in Britain.

Rank and File Committees, building on the earlier Minority Movement, were established in many ports, and unofficial strikes took place in 1947, 1955 and 1960.

Seafarers could be away from home for months or years and so "a union man" on board, not far off in the Clapham headquarters, enhanced solidarity.

It was widely supported by union members and caused great disruption to shipping, especially in London, Liverpool and Southampton.

The political importance of the strike was enormous: the disruption of trade had an adverse effect on the United Kingdom's (precarious) balance of payments, provoked a run on the pound and threatened to undermine the government's attempts to keep wage increases below 3.5%.

The Labour Prime Minister, Harold Wilson, was strongly critical of the strike, alleging that it had been taken over by Communists to bring down his administration.