Firstly, any party candidate who wins a first-past-the-post (FPTP) constituency in a federal election would be elected as an MP, no matter how few party votes the party won.
On that basis alone there would be quite a number of SNP MPs in the House of Commons.
Secondly, parties can qualify for a share of the list seats by two different criteria: either by winning at least 5 per cent of the national vote or by winning at least three of the FPTP constituencies.
While the SNP would not have qualified by the first criterion, they would most certainly have qualified by the second criterion.
That would have given the SNP some more MPs, as I explained in my earlier letter (19 May).