Urghh. As I understand it I don't think you're obliged to allow any viewings, but regardless it's not good when that happens. Especially if you've got some amateur of a landlord who breaks their word, might disagree about viewings and expects you to comply. What a hassle, even just speaking to the landlord or their agent on a regular basis during such a process, never mind the viewings and all sorts of concerns there.
I didn't reply earlier because I was trying to find the post in which you'd expressed how happy you were living in your current place. I can understand you not being happy with this turn of events.
Yes we do like the place. It wasn't going to suit us long term but another 6-12 months would have been fine. As I understand it you can make yourself into a pain up the **** when it comes to permitting viewings, but that's not really my style, as long as it is genuinely convenient. I've also managed to negotiate a slightly longer notice period (if he does find a buyer) so that will help us move. It's just inconvenient with both working, a baby and a toddler, summer hols scheduled etc.
Very unlikely we'll move into another rental to then move again into a purchased place so I expect to be flinging some lowball offers in a number of directions shortly.