Going back into recent history in 1979 there was a a referendum in Scotland on the 1978 Scotland Act. This act would have given Scotland much of the powers that it has now. The requirement then was that at least 40% of the TOTAL registered voters in Scotland had to agree to the Act to make it law. In the end around 60% of the voters voted and of those just over 51% voted for the Act. This did not met the 40% of the voting role requirement so Scottish self-rule went on the back burner for a decade.
The 40% rule meant that if you could not be bothered to vote then it was effectively a 'NO' vote; something a lot of people took advantage of. In theory if those people had got off their backsides and voted 'NO' then a majority in favour of the Act would not have been achieved.
Because of the way the then Labour government had organised it they lost the support of the few SNP MPs in Parliament and the Callaghan government fell; and was replaced by Maggie Thatcher.