In case it helps anyone this is what I discovered and had to do to sort myself out.
There is one key and only one key that will allow you to ssh into the instance. That key is the first key.
Subsequent creating keys is a waste of time they will not let you ssh in.
As soon as you get the key ( the first key see above) chmod it... One of the issues I had was that I tried to use a key with that had too wide a permission. I am convinced that doing that led to that key being blacklisted at the AWS end and so it became useless. I may be wrong but once bitten. ..
In the end I exported my WordPress website from the first instance, created a new instance, downloading and carefully saving the key which I was now aware was the one and only key which would give me ssh access. I deleted the first instance followed by importing the website to the second instances WordPress install.
AND IT WORKED...
Well almost, I had some issues with some of the media as it seemed to be indexed to the first instances up address but a bit of tweeking sorted that.