Everything you need to certify a copy of a lasting power of attorney: two ready-made COLOP C40 self-inking stamps, one for every page and one for the final page. Both carry the wording GOV.UK asks for, so there's nothing to write out by hand except your signature and the date.
Every page: our every-page stamp (“I CERTIFY THIS IS A TRUE AND COMPLETE COPY OF THE CORRESPONDING PAGE OF THE ORIGINAL LASTING POWER OF ATTORNEY”). Stamp the bottom of every page of the copy, sections 1 to 11 and any continuation pages
Final page: our final-page stamp (“I certify this is a true and complete copy of the lasting power of attorney”). Stamp the final page as well, so the last page carries both statements
Sign and date: both stamps have Date and Signed lines. Sign and date every page by hand. If the LPA isn't registered yet, don't stamp sections 12 to 15
Who can certify: a solicitor, a notary (someone authorised to carry out notarial activities), a chartered legal executive or a stockbroker, or the donor themselves if they can still make their own decisions, under the Powers of Attorney Act 1971 s.3 and GOV.UK guidance
Size: 58 x 22mm rectangular impression on each stamp, COLOP C40 self-inking stamps
Ink colour: both stamps in the colour you choose above (Black, Red, Blue, Green or Violet)