HeathrowAirport,
I read your first post, then the second one and promptly skipped everything to the end.
One of our jumbos on a long distance flight (full tanks) entered the runway and some (a very small amount of) fuel escaped from the fuel vents on one wing. The next aircraft (not local airline) to line up got a bit 'over excited' by the fuel and reported it to tower who in turn shut the runway. Delay as a sweeper was found to clean up fuel...Fuel had actually almost all evaporated by the time sweeper arrived.
No big event. Aircraft that spilt the fuel was informed of possible 'fuel leak' but replied that it is normal and they were carrying a large amount of fuel.