I'm astonished that anyone would think a 14mo baby is 'badly behaved'. I've had four children and now have three GC and have never considered a 14mo as 'badly behaved'. Yes, they do things you'd prefer they didn't, but they're exploring the world because it's fun and exciting. If they're doing something you don't want them to, then divert their attention. Saying No to them is exactly the reaction they want and of course they'll repeat the behaviour if it provokes a funny response from you.
Hitting children, whether you call it a clout or a tap or not, isn't the answer. I admit I occasionally smacked my eldest, because I didn't know any better in those days, (and I'm not proud of it) but not my youngest because by then I knew there were better ways to discipline children than by hitting.
It's not a great example to set children, and I wonder what the reaction would be if a child who had been hit then went to nursery and hit or bit another child because they were doing something perceived as naughty.