The short answer to the…
The short answer to the first question is that I'm not sure where the unusual precipitation patterns in the UK came from this year. Under a typical "negative NAO" pattern, we would expect cold and dry conditions there. From a quick look at Jan-Mar circulation patterns, while the SSWs helped promote a blocking high pattern over Greenland, the NAO pattern was actually weakly positive over these three months. In addition there was a high pressure ridge over North Africa. This may have helped promote water vapor transport northward to the UK. However, this is overall speculation on my part, and actual attribution would need to be done more carefully! For the second question, yes, there does seem to be a reappearance of the negative AO/NAO since the end of April, which is likely associated with the change in winds you see. This could still be an extended influence of the SSW, but again it's difficult to say for sure without more careful analysis.