Alexium trading - 27/08/15, page-31

I think those big orders usually sitting sitting outside of the trading window are mostly transient and are part of the toolkit of the insitutional players and meant to add some pressure to us retailers in the main. If they were genuine they would be using algorithmic trading to achieve the same result with less disruption to the order streams or would be part of some cross or dark pool trade..

They have another trick which is to scatter more modest but substantial sell orders, say 50K or 100K parcels, in price increments also outside the trading window. They are not quite so obvious when done this way and they pretty much always disappear overnight just in case they get caught in an opening gap I would guess.