Nurofen have stated that human error is the most likely cause, but have refused to rule out sabotage, giving DM a green light to wade in. While it's perfectly possible this was an animal rights action, the DM agenda is blatant and cynical.

In a very brief skim of various news outlets, it appears that the breakdown is:

1) Some reporting the story as a suspected wholesaler error without mentioning animals at all.
2) Some reporting it as a likely wholesaler error but pointing out that sabotage hasn't been ruled out.
3) The Daily Mail, who as far as I can tell are alone making claims about animal rights involvement with absolutely no reason given for this leap.
4) Some mentioning the DM claims in their reports, but not reporting them as fact - just DM conjecture.

So it appears to me at least that DM have plucked this animal rights claim out of their arses as usual. It's only strange they didn't blame looters and immigrants too.

 http://www.dailymail.co.uk/health/article-2030126/Nurofen-plus-recall-Animal-rights-protesters-suspected-painkiller-sabotage.html