I hate to disappoint you guys, but flatulence (the human type) has very little methane in it. It's mostly hydrogen, carbon dioxide and stinks because of volatile fatty acids, amines and other stinky things like indole.
Now cows,...... they are great belchers of methane and hydrogen and carbon dioxide. Great Britain is not an agricultural powerhouse and their cattle since mad cow are probably depleted, but pre mad cow, if you hooked all the cattle in GB up you could fill the Hindenburg in a 24 hour period.
However, this still is great news if it leads to the discovery of even a very meager presence of life on Mars.
GREAT NEWS!!!!
It's difficult to have one of my core beliefs shattered.