The person of interest appeared to have died in 2001 and there may be grant of probate and will for this person. You can search here.
https://www.gov.uk/search-will-probateA google search also reveals that you have been looking for this person and his mother for sometime, including posts on Ruislip Reunited and the letters page of Get West London which includes her married names and the name of another child.
If I were on the receiving end of a letter written to me in the capacity of informant on a death certificate (either as family member or medical professional) and you are not a family member, I wouldn’t respond.
You should be sending this information to his putative father and get him to write to the informant and apply for a copy of the grant.
With the further passage of time since his death, you should be hesitant in contacting anyone named in the will. Leave it to his birth family.