The pair are currently at the centre of an elder abuse storyline which has seen Rachel Breckle (Gemma Oaten) express fears that Ashley is mistreating Sandy (Freddie Jones).
Ashley's angry behaviour comes as he continues to struggle with the fact that his wife Laurel (Charlotte Bellamy) fell in love with Marlon Dingle (Mark Charnock) last year.
Middleton told itv.com: "Tensions have flared to the surface recently because of what's happened between Laurel and Marlon. The thing that is deeply hurtful about that is he knows they fell in love, and Ashley's been knocked for six by that.
"Ashley's been trying to make the Thomas household perfect," he continued. "You can't do that, but nevertheless that's what he's trying to do, because he wants the relationship between himself and Laurel to get back on an even keel.
"He wants to provide, he wants to protect, but he mainly wants Laurel to stay. Any threat to that at all is a threat to his marriage, and that's how he's beginning to regard Sandy.
"He's wrong, and it leads him to do things that are very unprovoked, dangerous and cruel. But he's been driven to it by the pressures that he feels."
Ashley fears that his reputation could be destroyed next week when social services become involved in the situation. Although the authorities later report that they have no concerns about Sandy, how long that stays the case remains to be seen.
Middleton added: "For it all to be shattered now would be devastating - goodness knows what would happen to Ashley. It's going to be really interesting to find out. We're going to see some big changes."
Emmerdale airs weeknights on ITV1.
> Emmerdale spoiler pictures - Sandy left injured by Ashley
> Emmerdale Gemma Oaten: 'Ashley, Sandy abuse plot is heartbreaking'
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