It should not be expensive to have your local solicitors certify a document as being a copy you may need more than one copy so worth having a number done. A commissioner for oaths is appointed by the Lord Chancellor to administer oaths or take affidavits, by statute every solicitor who holds a practising certificate has the powers of a commissioner for oaths but many do not exercise these powers where they are acting for one of the parties.
The original certified copy should be sent.