if i buy the lastest iphone from japan and bring back unopened will it work in as normal when i get back to london

If its unlocked, yes.

Though note Japanese iPhones have government mandated restrictions that cannot be removed such as the Camera shutter sound being permanently turned on and loud.

Also note, that warranty will only be valid in Japan, and you will need to return it to Japan physically to have it serviced under warranty. Apple does not take international shipments for service.

I believe that in the U.S., most iPhones purchased directly from Apple now come unlocked. (There may have been one exception to the rule if you financed the phone through a particular carrier.). But go somewhere else, and you still might get a carrier-locked phone.

As far as the Japanese shutter sounds are concerned, Google search found this:

https://www.photographytalk.com/photography-articles/8053-why-all-cell-phones-in-japan-are-shipped-with-an-annoying-shutter-sound

https://www.jluggage.com/blog/lifestyle/japan-shutter-sound-law/

If bought directly from Apple it should be unlocked. If bought from a Japanese carrier or other store it may be locked or require activation on a local Japanese carrier at which point it may lock to that carrier.

Help67atme wrote:

Many thanks

i thought all new iPhones came unlocked,I wonder what the deal is with camera sound

The requirement for the shutter sound is common in Asia, I know it's a requirement in Japan and Korea. Its purpose is to discourage people from taking photos without their subject's being aware.

I would say no you would have to replace the sim card to get it to work here in the states but I could be wrong but going to Japan you can change the SIM card and your iPhone will work in Japan so if you buy a phone in Japan it should work the same here