I handed my notice in last week (3 weeks on top of my 4). I attended a meeting this week with the MD and my manager to discuss my options & to run through my role. After the meeting I had verbally accepted to stay but having had time to digest the offer have decided it is in my best interests to move on to bigger and better things. How can I approach this subject and retract my acceptance of the counter offer??
Be straight up about it as soon as possible, tell them basically what you said here. Upon reflection you feel that moving on is better for you. There's not a lot they can do about it.
You have already handed in your notice.