Warhurst was a
The unofficial strike by 4,000 Dockers at Hull (and Goole) of August 1954 revolved around filling or scuttling method, this involved dockers standing up to their waist in loose grain in the confined, sweltering hold of a ship, shovelling grain into individual bags using big metal scoops. In 1959, Warhurst was to rejoin the "white" union, the TGWU, eventually becoming a full time TGWU official, and finally returning to dock work in the 1970s.
The reason given (By Keith Sinclair) for CP members opting to join the allegedly more radical (certainly more democratic) Blue Union (NAS&DU) at Hull, when the line from the Party centrally was to remain within the TGWU, was said to have been that unlike Liverpool & London Communist dockers they were less "political integrated". It is also likely that the division between the right wing full timers and the dockers, and importantly the dispute itself (scuttling) was more in intense than at other ports.
The NAS&DU finally amalgamated with the TGWU in 1982.
Source: `How the Blue union came to