Not saying that Kawasaki is any better than Boeing, for all I know the Poseidon might be a better fit than the P1, it certainly has some strong selling points like the fact that it is a 737 and therefore lots of parts, people and knowledge is readily available already.
Just saying that if the UK opts for the P1, the industrial offset possibilities must not necessary be a problem.
I do think that the P1 is that much better looking but I don't really know anything about what makes an MPA a good MPA, I do think that the Japanese have a vested interest in having the best of the best when it comes to Maritime defence related stuff so it probably is good enough for the UK too, just like the P8 probably is.