Tappers Dad
Not sure which aircraft it was or what the problem was, however the following are several reasons why this could have happened: The landing distance available at Gib is somewhere around 5700 feet. This is not very long for a heavy aircraft to stop on before either the brakes fail and/or it goes for a dip in the Med. If the aircraft had a problem that required it to be landed sooner rather than later, fuel would have been deliberately dumped to reduce the all up weight during its positioning for an approach. Nimrods are also notorious for venting fuel when the tanks are reasonably full, particularly when it is warm (eg Gib in July). It is therefore possible that the fuel "leak" may have been normal venting that continued after the aircraft landed.
Of course, it could have been a large fuel leak.
Hope this helps and sorry I don't know what actually happened.