You are asking if you need an official confirmation to this? If so, then the answer is yes. Legal and official authorities may not recognise a deed poll as a valid document, therefore an official declaration should be made. This is not a "real" decument in these respects, although it may be accepted sometimes - it just depends where (be more specific).
Olaf that is incorrect, stop misleading people who want advice... If you have a pesel number all you need is to fill out a application stating you have changed your name stating the reasons why..this will be endorsed on your pesel... good luck