You can't split them, propagation is by basal cuttings or seed, sometimes root cuttings.

I found a site on the internet that said you could and I was told on this site that you could split them like hardy geraniums. Ive yet to do mine as it was recommended to be done in the Spring. Now I am wondering if it is the right thing to do?

My answer hasn't changed from the one given previously, regardless of what you've read on the internet or elsewhere. Info taken from RHS Encyclopaedia, Reader's Digest Plant Encyclopaedia. Up to you what you do though.

The 'Expert' series of books says that dividing clumps in spring is OK.

Guy from the Telegraph shows how (though the pics & instructions are not in sequence) here :

http://www.telegraph.co.uk/gardening/gardeningpicturegalleries/7538042/How-to-divide-and-replant-delphiniums-in-pictures.html

Though the lady from the BBC says this is the only way to propagate :

http://www.wonderhowto.com/how-to-propagate-delphiniums-campanulas-and-lupins-264499/view/

So it seems opinion is divided........

I did divide a couple of 4 year old plants into 3 each a couple of years back and they are all doing fine - maybe I got lucky

I've never tried splitting them - I find the slugs finish them off in the spring before I realise it, so never have them more than one season, lol!