"From now on all rumours must be attributed to Alan Fridge!! BBC mole, Cardiff insider—Alan Fridge!!!"
—Steven Moffat (personal friend of Alan Fridge), Outpost Gallifrey Forums, 6 August 2007
Last year, a tabloid newspaper published a rumour that Jenna Coleman (who plays Clara) was leaving Doctor Who. It was, of course, complete rubbish, Jenna was quick to make it clear that she wasn't going to answer the question either way, since it was a goldmine of free publicity - something that the rest of the cast, crew and publicity department got on board with. Just before Christmas, when the fact that Jenna was staying couldn't be kept secret any longer, the rumourmonger tried to save face by claiming that she'd had a last minute change of heart, and that the ending of _Last Christmas_ had been hastily rewritten to accomodate this. However, the ending certainly didn't look tacked-on.
So who is Alan Fridge? My theory is that he's a low-ranking member of the production team, a runner or somebody like that. He's around a bit during filming, and picks up things like the row between Clara and The Doctor in _Kill the Moon_, or the old Clara scene in _Last Christmas_, but he doesn't have the big picture. He leaks information to the tabloids to make himself feel important, and probably for a kickback.