The last time a left wing Labour Party won a majority (+3) was 45 years ago. Tony Blair moved the party to the centre in 1997 and won three in a row.
I get that he wasn't Labour Classic but that was still 13 years when the Tories were out of power.
To be honest though I think we've seen the last Labour majority anyway given the electoral map in Scotland. I think any future non-Tory government is a Labour/SNP coalition.
In fact if I were Boris right now I'd be handing a second independence referendum to Nicola Sturgeon on a silver platter.