It is not known when this term was created. Slut is a curse used to specifically offend women, and dosh is a slang that the British use to refer to money.
It is much used to offend a woman who owes money to you (or who owes money to anyone else), but it can also be used to refer to prostitutes.
"I hate that Slut-dosh!"
"She owes me money too"
"Stop looking at the Slut-doshes!"
"I can not! Some are very flashy..."