Jonny,

How would you intepret third sentence (six month requirement) and how does it apply with a B2 holders who is already here for 6 months and is on approved extended stay of another 4-5 months?

3) A valid airline ticket for travel via the United Kingdom as part of a journey from Australia, Canada, New Zealand or the United States of America to another country or territory, provided that the transit passenger does not seek to transit the United Kingdom on a date more than six months from the date on which he last entered Australia, Canada, New Zealand or the United States of America with a valid visa for entry to that country;