p1M Knitting Abbreviation

Hi - Just started a new pattern (Urban Throw purchased on Ravelry) & there is an instruction I haven’t seen before. It’s p1M. I have googled to no avail. It’s a UK pattern, but even the UK abbreviations do not include this one. I, at first, assumed it was a variation on placing a marker, but it doesn’t seem to really fit. Stumped… Any ideas?

Thanks in advance!

Welcome to KnittingHelp!
Purl one, Main color?
Can you quote just one line that uses the abbreviation?

Yes! That was it. Thanks!