I haven't heard mention of any special connection between Linode datacenters. As far as I know, traffic just goes over the regular Internet. If what hybinet describes (ISPs restricting bandwidth to sites outside Japan) is the cause, going through the Tokyo datacenter might help. But if it's just general congestion, it probably won't.
You can do a quick test using just SSH on a London host and a Tokyo host. Configure your web browser to use a SOCKS proxy on localhost, port 1080.
Condition 1: run
ssh -D localhost:1080 user@your.london.linode from your home machine, and log in to the London host. This is your baseline.
Condition 2: run
ssh -L 1080:localhost:1080 user@your.tokyo.linode from your home machine, and log in to the Tokyo Linode. Then from the
Tokyo Linode, run
ssh -D localhost:1080 user@your.london.linode and log in to the London Linode.
If Condition 2 gives you better results than Condition 1, that's an indication that what you're talking about might be worth pursuing. This method is not necessarily the most efficient, as all traffic is being encrypted and decrypted twice along the way. But it may serve as a rough idea of whether you can gain anything.