when they PHM were discussing to put Ash up he was very guarded. He was weighing up the options of this being shown to the house and as he is so scared of Helen and Ash
he was already planning how he could get out of this if it was to be shown. I think he really did want Ash up but as he said "The shit will hit the fan when they find out and I cant take on the both of them" I think some people heard this as "I can take them on " but he actually said "i Cant". Mark is terrified of that duo, I think he would get them out if he could get away with it, i dont think he likes either Helen or Ash but I think this betrayal of Chris and ashleigh will have devastating effects on his chances of winning now.

I thought he said he can take on both of them

No he said I can't take them both on!

he deffo said he cant but his accent does make it sound otherwise.

Mark = The smiling assassin.
Watching him tell Ash that he was in tears when he put him up for eviction, which clearly wasn't true, should really kill his chances of winning BB stone dead.