It comes after Simon confessed earlier this month that his decision to hire Alesha was mainly to annoy the BBC.
"My decision to poach her was 70-30 on the fact she was on Strictly and the fact I liked her," he said.
The music mogul, who will also be judging Britain's Got Talent this year, added: "With us and the BBC, I laugh about it, but there is unbelievable rivalry now. They want to be number one, I want to be number one. We do what it takes."
But Len hit back this week, moaning: "I would never knock the opposition and I think it is spiteful and mean if that is the case that Simon said 'I just want to be spiteful towards Strictly'.
"Because why would you want to do that? Why would you want to spoil millions of people's pleasures? It's not the right way to behave, so if that is the case - shame on you, Simon."