hi i have some 119mm round edge skirting (pencil round?) to fit. should i cope internal corners with this and what adhesive do you recommend to fasten skirting to plasterboard walls?
"Cope" is an American term and is not used in the UK. So scribe the internal corners (it isn't hard with pencil rounds and allows you to deal with out of square corners, too). I've seen butt and fill the gap a few times and frankly I think it looks terrible.
How are you securing the skirting? I'm trade, so I'd normally use a 2nd fix nailer with a grip adhesive such as GripFil or Pink Grip. I found that on metal framed walls that won't always work so I have also used low expansion foam per advice from @foxhole (who has repeatedly recommended this)