I can't help but think that the Japanese requirements for maritime surveillance should be very much like our own. Both island nations surrounded by sea, off a major continent where there are/could be problems emerging. So surely the P1 could well be set up pretty well exactly as we would want it - as it comes off the production line?
You're not making the mistake of believing that an aircraft would be selected chiefly for its technical merit, are you? The P1 no doubt has various merits but how many British jobs depend either on that airframe or the relationship between our Govt and the nation whch produces said airframe?
Umm, what are those big grey helicopters I see buzzing around the skies most days?
That's right - the ones that have just been upgraded to keep them at the top of their game, having taken over from the Sea King quite some years ago!