The elections watchdog has agreed to rule changes after it allowed a right-wing party run by a former Swanley BNP councillor to use a slogan featuring Lee Rigby.
The Electoral Commission gave the green light for Britain First to use the description "Remember Lee Rigby" on voting slips for this month’s European elections.
The party is run by Paul Golding, who resigned as the BNP’s Sevenoaks District councillor for Swanley St Mary’s ward in March 2011.
Although the slogan cannot be used in future elections it can still feature on ballot papers in Wales on May 22, which is the first anniversary of Fusilier Rigby's death.
The 25-year-old father-of-one was murdered by Islamic extremists in Woolwich nearly one year ago.
Electoral Commission chairwoman Jenny Watson apologised personally to members of Fusilier Rigby's family in "difficult and emotional calls".
The report of the independent review into the decision said: "It should be noted that each call confirmed that the use of Fusilier Rigby's name in a party description had caused deep offence and distress."
Britain First applied to use seven slogans in the elections and four were rejected but the remaining three, including the one relating to Fusilier Rigby, were approved by the watchdog.
The commission's director of party and election finance Peter Horne, who has now resigned, "remembered thinking that it was distasteful but not sufficient to cause offence", the investigation said.
Although the review found the staff involved acted largely within the commission's processes, they failed to consider any need to protect public safety, morals or the rights and reputations of others.
Elizabeth Butler, the independent chairwoman of the commission's audit committee, carried out the investigation into the decision.
She says the watchdog must introduce checks when personal names are used in party names or descriptions to ensure the individual or their family has consented and review all names, descriptions and emblems currently on the register.
Ms Watson said: "The commission is deeply sorry for this mistake and the pain that it has caused Fusilier Rigby's family.
"The commission welcomes the report of the independent investigator and has accepted all the recommendations that have been made.
"These will now be implemented as quickly as possible to ensure a similar mistake is never repeated."