Here's what I would do:
No. 8 sds drill bit, you can buy longer ones. Start drilling, without hammer action on, when you get to brick, hammer on and drill to about 3-4inches deep. Here's the important bit, tap plug all the way in, use a 2 1/2 "- 3" no. 8 screw and you should get a good tight fixing.
Doing it this way you avoid brittle crumbling plaster.