just a couple more thoughts on your situation. firstly, i think you will have to check with immagration about continually leaving for a couple of weeks for getting permanent residence as it's either 3 or 5 years continuous living in Japan. i don't think it's a problem with an ordinary 1 or 3 year spousal visa. you just need to get a multiple re-entry visa or whatever (Y6,000 for 3 years). actually you need a visa to get back in even if you're a permanent resident, but p.r. status is good for life i think.
also if you girlfriend wants to work as a nurse in the UK, i believe she will have to do the UK nursing exams before she can get a job, so would need pretty good English.
then there's also income tax status, which country....
my situation was a little different as i lived with my wife as a girlfriend for 5 years in 3 different countries before she said she was coming back to Japan permanently. i didn't have any property in the UK or elsewhere, but i was earning good money as a freelance programmer and i gave that up when i came to Japan. my wife's parents are successful business people and gave me and her jobs when we first came, so i was in Japan for all the time except for a couple of weeks before i got permanent residence. if you decide one day to settle down in Japan, you would have to give up a lucrative job in the oil business and probably settle for teaching English or perhaps you and your wife could start a business up.
anyway good luck !!
