Unilever are one of the worlds largest practioners of vivisection, and have been subject to an ongoing concerted and coordinated campaign of protest from PETA.
The 'spurious' complaints of offence to OFCOM regarding this advert are simply another arm of this protest.
Personally I strongly object to vivisection for commercial purposes, but support it whole heartedly for medical research.
From my knowledge of PETA their views are as extreme and intolerant as those they protest about .... and in this particular case they've given Unilever and Marmite an unexpected commercial boon, whilst shooting themselves in the foot.
.... oh, and I can't stand Marmite.