pronunciation - When did Greenwich begin to be pronounced as "Gren-ich"?

I just read an interesting question here on Greenwich Mean Time.

I'm interested to know when Greenwich received its peculiar pronunciation. Has it always been pronounced as "GREN-ich" (/ˈɡrɛnɪtʃ/), and is it just a simple contraction or something more?

I'm from Northern England and would say that GREN-ich is used nationally and globally, but I agree with Wikipedia that I've heard it pronounced GRIN-ich in London.