A Father's Day theory of Relateeveety......
Gabe Kelly was a black American soldier stationed in England after World War II ended. He fell in love with an English girl named Mandy Dean and she gave birth to Gabe's daughter. This resulted in her being shunned by her own family.
After Mandy was found murdered, Private Kelly was under suspicion for a short time as her killer, but it turned out to be another soldier who was responsible. Gabe was redeployed but planned to come back for his daughter once he was cashiered out of the armed forces.
His original plan with Mandy was for them to move to Harlem in New York City, but it's the belief of Toobworld Central that upon becoming a civilian, Gabe Kelly instead chose to relocate to England. That way, his daughter could grow up in the country where she at least had a possible chance to become acquainted with her grandparents. (That wasn't very likely based on what happened in the episode, however.)
Once she did grow up, Gabe and Mandy's daughter married and may have moved to the Norfolk town of Market Shipborough*. One of her children, most likely her youngest, was named Anthony. He grew up to join an elite horse guard in the British army. Unfortunately he lost part of his leg in Iraq, but with help from his lawyer Peter Kingdom, Tony was able to rebuild his life in Market Shipborough.
This theory of relateeveety connecting 'Foyle's War' to 'Kingdom' is speculation and not to be considered an official part of either TV series. Both characters were played by Obi Abili.
'Foyle's War' - "Killing Time"
'Kingdom' - [Series 3, Episode 1]