A method I use, which gives a good class of job, is to hold the skirting level on the floor, and pencil a line on the plaster along the top.
Snip it off with a hammer and bolster (it may be ragged) and screw a wooden batten level so that the top of the batten will be level with the top of the skirting. Clean away any plaster or mortar snots remaining below the line. You can space the batten off the wall a bit if you want, it is best if the batten is flush with the finished plaster.
Patch the plaster down to the batten.
Use another batten an inch or two off the floor, spaced to be flush with the first. Clean away any plaster or mortar snots remaining below the line.
You can paint the wall, and let the paint lap onto the top batten to help conceal anything that might show.
When ready, you can screw the skirting to the battens. The battens are firmly screwed and give good support, the skirting only needs small screws into the battens. I suppose you could glue it. Screws make it very easy to remove if ever needed. If you suspect residual damp, treat the battens before fixing and use rust-resistant screws.
The space between the battens can be used for aerial, alarm, phone, speakers or LAN cabling (but not electricity as it is concealed and not in a safe zone).