Almost immediately the SLP became the focus for entryism from the International Marxist Group (IMG) and at the party's first congress in October 1976 the IMG were expelled.
The SLP had little electoral success, winning only three council seats and polling only 583 votes in the Garscadden by-election in 1978. At the 1979 General Election the SLP fought three seats, including Sillars' attempt at being re-elected (Robertson chose to step down). Sillars came close to retaining his seat, but this was clearly a personal vote built up over the years he had already served as a MP, as the other two candidates polled very poorly indeed.
This failure prompted the SLP to disband and members either fell out of active politics, re-joined the Labour Party, or chose to join the Scottish National Party (SNP), which both Sillars and Neil did, with both rising to high office in the SNP.
The SLP adventure is generally looked upon as an ambitious failure, but Sillars has himself put this down to a lack of planning before choosing to launch the party. Unlike the SLP the Social Democratic Party (SDP) meticulously planned their breakaway from the Labour Party and this proved to provide for much more success. Sillars has claimed though that the SLP did at least provide a forerunner to the SNP's later dialogue with the left.