A deed is a written legal agreement that has been signed and delivered (that is, shown to all concerned parties). Poll is an old English word used to describe a legal document that had its edges cut (polled) so they were straight. This was done to visually distinguish between a deed signed by one person (a polled deed – hence the term Deed Poll) and a deed signed by more than one person (an indenture), which had an edge indented or serrated. Interestingly enough, indentures were originally written twice (side by side) on a single piece of parchment, which was then torn down the middle and each half given to each party. The impossibility of matching the tear was a guard against forgery.
Deed Poll documents for a change of name can be traced back to 1851 and can be seen at The National Archives, which is situated at Kew in Richmond, Surrey.