Flat exchange

I'd like to move to Tokyo for 3 to 6 months and would like to see if it's possible to do a long-term flat exchange with my flat in London. Can anyone recommend a website or any other resources that link people who want to do a flat exchange between London and Tokyo. All the flat exchange websites I've looked at so far do not have many Japanese users. Any suggestions are welcome.
thank you in advance.

i do not know the terms of "flat exchange".
do you want to have home-stay or exchange your room for anyone's room in japan?

In practical terms flat exchange means that if you live in Tokyo and you want to go to live in London i.e. for 6 months, you can find a person in London who wants to stay in Tokyo for 6 months and the two of you swap flats. This means that you don't have to go through the hassle of renting out your flat at home and renting a flat while abroad. So basically you help each other out. Have you seen the movie called 'The Holiday'? with CAmeron Diaz - that's what they did.

thank you for your explanation.

generally japanese don't do it 'cause most of landlords decline subleasing and most of japanese are timid and worries about troubles .

But some people might want to do it.

many japanese want to be taught english by native speakers. so you can find them on websites or skype and you can offer it.many people will beg off it. but don't give it up.　

I can't help you with that particular exchange but a friend of mine did that with a French family and it took her quite a while to set up the whole thing (she and the French family agreed in advance that they both would do what is explained below) .. .
Basically you need to make a binder explaining all about your place, how appliances work etc. also give emergency numbers about all sort of things etc. plus have photos and maps of the neighbourhood, mention your favorite grocery, baker, etc.
The major thing--and the hardest--is to "coerce" friends into welcoming the foreign party on arrival, showing them the home etc. then calling on them 1 or 2 days later, to "get your mail"..and also take them out. this is both a nice gesture but also a security measure.
Did you check: http://www.1sthomeexchange.com/browse-Japan.php