Looking at a house, end of a row of three terraces. It has dormer/loft conversion, as has next door, but I think I'd want to stick a Velux in the front aspect for more light. Next door hasn't got one. Would I need planning permission?

depends on the local authority, but generally yes you would.

Hmm I thought it was a building regs issue unless its a conservation area..

You generally don't. You will if the house is listed or in a conservation area or a top floor flat IIRC.

edit: look here: http://www.planningportal.gov.uk/england/public/buildingwork/projects/workcommonroof/

i stand corrected. 😳