The demise of the SLP was ultimately the result of same condtions that led to the demise of the ULA. Neither group attracted new fresh layers of working class activists that could fill out the party and reduce the perpensity for the component groups to come into conflict.
In his glossery of the left in Ireland, John goddwillie describes the SLP in the following terms
“formed in 1977 following the Independent (anti-coalition) Labour election campaigns. Attracted much uncommitted support and also the League for a workers’ Republic, Irish Workers’ Group, part of the Movement for a Socialist Republic, and the Socialist Workers’ Movement. These groups departed over the period 1978-80. The party has become fissiparous from the beginning, alienating its members for diverse reasons, and eventually dissolved in 1982.”
By 1979 without an influx of new fresh recruits the component parts – primarily the SWT and the IWG – degenerated in sectarian infighting.
At the time of the establishment of the SLP, the Militant argued that the move was tactically wrong – that it handed the LP back to a right-wing that had been badly weakened by coalition and that the potential existed for the left to wrestle control of the LP from the right-wing gangsters around Corish and O’Leary. Instead the LCLL walked out and formed the SLP – and with it removing the most significant and influential section of the left of the LP and handed the LP into the lap of very grateful right-wingers.
The Militant argued that ther SLP would not attract new layers of activists and would inevitably decline and disappear. Indeed during an upsurge of workers militancy beginning with the post office strike in 1979 – the SLP made minimal impact on events.
As for Matt Merrigan – while he was to the left of many others (particularly the chancers running the unions today) – he was ultimately a trade union bureaucrat.