Reasonable price anyway, but if you're a new customer you can get 25% off with code VOU0475684 on a spend over £40 - therefore you must buy two to get the lowest unit price. I also got free delivery.
As a new customer you could also get £6.06 via topcashback.
That brings the total down to £23.94 or £11.97 per unit.
Edit: direct link that works: http://www.ocado.com/webshop/product/Isle-Of-Jura-Single-Malt-Whisky/46777011