So Mr NDN has just been round!!
He was really apologetic about the whole thing and said things have blown totally out of proportion.
He told me that when I had parked across their drive the other day the Nanny had phoned Mrs NDN straight away at work to ask what to do about it and during the call, according to Mrs NDN, the Nanny had repeatedly kept saying she'd only parked there because she assumed I'd been at work and had seemed quite upset.
When the NDNs came home the Nanny was a little tearful and spoke to them about that I'd said to her and Mrs NDN had not been impressed hence why she then shouted at me. However, Mr NDN said in all honesty the reason for the Nanny's upset wasn't because of what I'd said to her but because of the difficult position that Mrs NDN is always putting her in regarding not being allowed to park on or across their drive which then resulted in all this fall out. Mr NDN said he had no problem with the Nanny using their drive (hence why she was on it yesterday I imagine) but that his wife doesn't allow it.
Mr NDN said that when I was at their house and being shouted at by his wife, she wasn't whilst angry at me as such, but also a little bit angry at the Nanny for causing this drama but secretly mainly angry at herself because she knew none of this would have happened if she'd just allow the Nanny to use the drive. He acknowledged he didn't get involved in the argument and said it's because he knew his wife was in the wrong but he did apologise for not having stopped her. He said he hadn't realised when he let me in that his wife was going to kick off at me.
Mr NDN said that the Nanny had been round yesterday morning and told him that during her phone call to Mrs NDN about me having parked across the drive his wife had apparently been quite rude and dismissive towards her and told her quite threateningly to "make sure the car was gone" (as in my car) by the time they got home!! This had obviously upset/scared the Nanny and she'd felt in a very difficult position and that's why she was so upset.
He said the Nanny had not used the words threatening or aggressive to describe the conversation I'd had with her and it was just his wife who had decided to accuse me of behaving like that.
Mr NDN also said that apparently the Nanny really does have something wrong with her back. I tried not to think about him bending her over the kitchen units when he said that....
Anyway, so yesterday morning she'd gone round to talk to Mr NDN about it all as she felt unable to talk to Mrs NDN about it on account of her being crazy (my words, not hers) and whilst there she had again said she didn't know if she could continue working for them in light of all this stress. He said he had apologised to the Nanny and had assured her that he'd speak to his wife. He said the Nanny then came over again in the evening to say she was prepared to stay if Mrs NDN changed her ways and allowed her to use the drive.
When he was telling me about the Nanny's coming and goings yesterday it was hard to act like it was news to me seeing as I'd been logging her visits on MN all day 
Anyway, Mr NDN has given the Nanny until next week off to allow the dust to settle and he took yesterday and today off to see to the children in her absence.
He has told me that he's spoken firmly to Mrs NDN who has now agreed that the Nanny can use their drive so long as she gets her leak looked at which she has agreed to do whilst she's off.
He then apologised again for the whole fiasco and said he hoped that normal neighbourly relations can be resumed in time when things have settled down a little.
He said that yesterday the Nanny had offered to come round and apologise to me again but I told him, in light of all this information, that an apology is not necessary and that I would much prefer to put the whole thing behind us and move on.
I was a bit surprised he was 'dropping his wife in it so much' but he seemed to want to fully explain the situation rather than give me a half story and he did seem genuinely regretful.
I suppose it explains why he wanted to speak to me alone whilst Mrs NDN was at work yesterday and why they didn't come over together in the evening. I imagine Mrs NDN doesn't know he was planning on speaking to me this morning either.
So yes - what a roller coaster.
From my conversation with Mr NDN it seems that Mrs NDN is clearly a controlling nasty cow, that Mr NDN is a bit afraid of her and that the Nanny probably is the victim in all this because it sounds like Mrs NDN is pretty vile to her really.
During the conversation he implied he and Mrs NDN are both off over the weekend so I suppose the next interesting thing to see is how Mrs NDN will act when she sees me next.
But - I am so relieved that there's light at the end of the tunnel and that it appears we may get a happy ending to this thread!!!