A scout troop is being investigated by the police after its members shouted death threats and racist abuse at Jewish war veterans during a remembrance parade.

Dressed in full uniform, the explorer scouts, who were taking part in Remembrance Sunday service in Romford, Essex were heard to repeatedly shout "Let's kill the Jews" at Jewish second world war veterans.

The head of the scouts in the area has issued a full apology for the incident, which was witnessed by a senior policeman standing a few feet away.

A Metropolitan police spokesman said the Met was investigating two allegations of "racially aggravated harassment" involving more than one member of the Romford explorer scout unit. He would not say how many scouts were involved.

The Rev Lee Sunderland, who was taking part in the service, expressed shock after hearing the scouts shout: "Here come the Jews, let's kill the Jews."

Other witnesses said the racists chants were started by a boy believed to be 15 years old. One of the troop has since come forward and been interviewed by police. He has been ordered by the Scout Association to visit the rabbi of the Romford and district synagogue to apologise in person.

Jack Rose from the synagogue said: "They were boy scouts who are supposed to be true to their cause. Somewhere along the line someone has been completely stupid or they really think these things."

Rose said Chief Inspector John Harlow witnessed the incident. He took statements from other witnesses and delivered a stern reprimand to the scouts for their behaviour.

Paul Freedman, an 84-year-old Jewish former RAF pilot who laid a wreath at the service, challenged the scouts. "I was absolutely fuming ... I told them I was a Jew and I'd spent four and a half years in the RAF during the second world war, and that Jewish people had sacrificed so much for freedom," he told the Evening Standard.

The county commissioner of greater London north-east scouts, Dean Jefferys, issued a letter of apology to the synagogue. He said he was "shocked and appalled" and that all scout members offered their "most sincere and profound apologies".

"I understand that a senior police officer spoke to all of the explorer scouts at the time of the incident. All the young people were left in no doubt as to the seriousness of the remarks and the consequence of further such behaviour."

Simon Carter, a spokesman of the Scout Association, said the scout who confessed to starting the chant flouted the scouting ethos. "As scouts we promise to do our duty and to help other people. Clearly this child has not lived up to this promise."