I bought a pencil dress from People Tree a couple of years ago, lots of compliments on it, still using it for work.
I checked their website last year and couldn't find anything similar, but I've been back this morning and they have an abundance of work-friendly dresses, natural fibres, with sleeves, in their sale and elsewhere.
www.peopletree.co.uk/sale/women/dresses I've bought a few in their sale, really looking forward to trying them on.