Unfortunately whoever done it is clueless....
The back flashing isn't fitted correctly to the side flashing - https://gyazo.com/39ae6427a45de0ccfb5c06329a0c0365
The tiles under the bottom flashing have also slipped, no doubt they didn't secure them to a new batten... -...
Mortar isn't really used in valleys in Scotland anymore.
Your best bet is removing the tiles and installing comb-fillers - https://www.roofingsuperstore.co.uk/product/marley-eternit-eaves-comb-filler-62mm-x-1000mm.html - (You can get cheaper ones than this)
It's done terribly and probably by someone that took a 1 hour crash demo on the stuff.
https://www.fatra.co.uk/roofing-solutions-products/fatra-single-ply-membrane/fully-adhered/
Don't them or ask for your money back.