There is risk for both incall and outcall... to some degree. But an incall could obviously be categorized as a common bawdy-house and therefore illegal. I would assume the courts don't care what goes on during an outcall in the privacy of your own place provided it is with consenting adults. The risk of an incall bust is low... but far from impossible. Here was some more information on a Google search:
"Bawdy-Houses Offences"
The laws regarding common bawdy-houses are aimed at those people who own or manage such places. Since keeping a common bawdy-house is an indictable offence, the maximum penalty for persons convicted on this count is two years in jail. Penalties for other people involved, (i.e. customers and prostitutes) are not as severe; the other participants would be guilty of summary offences. Section a 197 provides a definition of the terms "place, " "prostitute," and "keeper" (Lowman, 1992: 64).
Since World War II, the places which have been involved in common bawdy-house offences are the residences of the prostitutes, "trick pads" (a location used exclusively for the servicing of a customer), and, most frequently, hotel rooms (Lowman, 1995: 338). The police are not required to prove that the place is used frequently, the simple "general reputation" is enough to demonstrate that acts of prostitution occur regularly.
Places such as massage parlours escape being prosecuted under the bawdy-house laws because the customer pays for a massage; anything that happens after that is agreed upon between two consenting adults. Any payment that the masseuse receives is, theoretically, without the knowledge of the proprietor and/or manager. Despite their sly modus operandi, several massage parlours have been prosecuted to the full extent of the law according to the this section of the Code (Lowman, 1992: 80).