To make a power of attorney, to certify you signature on a document or to certify a copy of a document you need to visit the Consulate in person, present your passport and pay the fee of £50.00 for a power of attorney, £20.00 for certification of your signature or a copy of a document (fees apply for foreign nationals only).
If you are acting on behalf of a company you should also present certificate of incorporation, memorandum, articles of association and official seal of the company and pay the fee of £100.00 pounds. If you are not a director or a secretary of the company you must also present minutes of the board meeting which empowered you to sign the power of attorney on behalf of the company.