In most case, a deed poll is not required when a woman simply wants to change her name upon being widowed to her maiden name. A marriage certificate and a husband’s death certificate certify the name change and act as a valid evidence. This will work because the marriage certificate displays her maiden name and will be accepted as a documentary evidence.
However, there might be a requirement of deed poll where the death certificate of husband and marriage certificate are not accepted as evidence (e.g.: financial institutions).
A deed poll is definitely required in case a woman wished to change her surname to something else except for her maiden name.