Proper sexual terminology for a Fox Hunt

The NYTimes, February 18, 2008, in an article entitled “Luxborough Journal Tally Ho! A Determined Crew Hunts for Fox Hunters” discusses some of the pitfalls of a group of people in England who seek to enforce the ban on foxhunting. In discussing their successes and failures they state:

“Losing cellphone contact with Mr. Tillsley, they paused to reminisce about earlier forays, such as the day they hid so well that they were flushed out by a pack of hounds. Or the times they have seen adulterous members of the hunt ducking quickly into the bush for “some rumpy-pumpy,” as Mr. Floyd put it.”

Now, in connection with “rumpy-pumpy” a disagreement has arisen in my office as to the sexual proclivities of the adulterous members that are being discussed. Does rumpy-pumpy refer to gay sex on the hunt? And, if it refers to heterosexual adulterous activities, shouldn’t it be humpy-pumpy?