Yes it has Celeste. Lost my Manky twang completely. Hardly surprising as I've lived the greater part of my life in the south. However, when I was at primary school, back in the 60's, our 4th year teacher recorded each of us reading out a favourite poem. When he played it back, I couldn't believe how bad I sounded. I started making an effort to improve my speech, even at the age of 10. Hearing the variety of different accents around me in Cheetham was, I think, what gave me my ear for languages.
Hubby has never lost his northern (Lymm) accent tho. What was funny was the way our Bucks born daughter used to speak to me in a southern accent but spoke to her dad in a northern one. She'd ask me if we could go to visit Windsor 'carsell' (Castle) but, when her dad came home she'd tell him about her tip to the 'cassel'.
I should add that, at times of severe stress, I have been known to lapse into Mankspeak - eg 'bluddyell!' It's not just the accent but also the intonation of that which goes sort of like this: ~~. When really pushed to the limit, I have also been known to emit that classic Manky swearword 'kinELL'!