Definition of "deffo"

I know for certain they′re not speaking to each other, that′s for deffo, not that I′ve even seen them in the same room over the last week to confirm their silence.

2003, Grace Dent, LBD: it′s a girl thing‎, page 45

‘An infection. Nothing serious. They′ll have some colour in them soon, for deffo.’

2009, Joe Stretch, Wildlife, unnumbered page

“Couldn′t say for deffo, probably at least fifteen years old, but I know they don′t make them like these any more for exactly the reason you′ve just seen. The security systems shite.”

2009, Stephen Leonard Lancashire, Immaculate Deception‎, page 271

Needles wilted under the force of Pegg′s demand, his eyes widened and he seemed to shrink in size, and I can′t say for deffo but I think he probably wet himself.

2010, Simon Pegg, Nerd Do Well‎, page 25

And I deffo don′t believe in me, cos I′m a proper knobhead, aren′t I, and always have been.

2009, Nick Leather, Billy Wonderful‎, page 12

It′s weird, but even though Dosser was only grounded for like two weeks, I was actually starting to kind of miss him, and I deffo would′ve loved to have gone for a good old-fashioned crow-hunt that Saturday afternoon, […] .

2011, Andrew Fitzpatrick, Strictly Legal‎, page 128

‘ […] And no giving in at the slightest whimper. Agreed?’‘Deffo!’ He couldn′t see my fingers crossed behind my back.

2011, Maggie Graham, Me and My Animals‎, page 142