Alli left the home of Denise when he was aged 13 after social services threatened to remove her children due to her battle with alcoholism.
Denise admitted that she suffered from a severe booze addiction, revealing that she was "hooked" on vodka, beer or anything she could get her hands on.
And she says it was only right to get him off the streets and into a safer environment.
Speaking to the Sun on Sunday, Denise said: “I knew that was the only way he could fulfil his dream of becoming a professional footballer.
“It was tough to give up my son but it proved to be his salvation. I’m so thankful for how things have turned out.”Alli was handed his England debut earlier this season and scored a scorcher in the Three Lions' 2-0 win over France at Wembley.
“When he scored the goal against France I leapt out of my seat — I was so happy. My son has made it by himself. I am so pleased for him and super-proud of everything he has achieved.”Although Alli was never formally adopted, he lived full-time with the family of fellow footballer Harry Hickford, now 20, six miles away.
Denise revealed that the move to Cosgrove moved him away from the children on the streets of his old estate, who were regularly "smoking, arguing and robbing".
And kind-hearted Alli helps out Denise too. She says that he has given the family around £4,000 over the past year, including Christmas, birthday and Mother's Day treats.