Fixtures (Pool C): September 22 – Tonga (Sapporo), September 26 – USA (Kobe City), October 5 – Argentina (Tokyo), October 12 – France (Yokohama).
World Cup best: Winners, 2003.
Knockout phase: England are likely to face Wales or Australia in the quarter-finals, whether they win their pool or finish second. Topping the group, and then winning the quarter-final, is likely to mean a last-four appointment with reigning world champions New Zealand.
Fixtures (Pool D): September 23 – Georgia (Toyota City), September 29 – Australia (Tokyo), October 9 – Fiji (Oita), October 13 – Uruguay (Kumamoto).
World Cup best: Third, 1987.
Knockout phase: If Six Nations champions Wales top a group that also includes Australia and Fiji, they are likely to meet France or Argentina in the last eight, and then Ireland if they progress. Should they leave their group as runners-up, then England and New Zealand loom large.
Fixtures (Pool A): September 22 – Ireland (Yokohama), September 30 – Samoa (Kobe City), October 9 – Russia (Shizuoka), October 13 – Japan (Yokohama).
World Cup best: Third, 1991.
Knockout phase: New Zealand or South Africa are set to provide Scotland's quarter-final challenge. If they win their group, it's probably South Africa, but progress as runners-up and the All Blacks are likely to block their path.
Fixtures (Pool A): September 22 – Scotland (Yokohama), September 28 – Japan (Shizuoka), October 3 – Russia (Kobe City), October 12 – Samoa (Fukuoka).
World Cup best: Quarter-final play-off, 1999.
Knockout phase: Ireland will be favourites to win their pool, despite a disappointing Six Nations, and they could expect a quarter-final against South Africa if that transpires. Should they then beat the Springboks, it could be Wales – their emphatic conquerors in Cardiff on Saturday – next.