Hi,
I totally agree with Capt Pit Bull.
Our MEL says something like "The provisions of the MEL are applicable until the aircraft commences the flight, i.e. the point when an aeroplane begins to move under its own power for the purpose of preparing for takeoff.
Any decision to continue a flight following a failure or unserviceability which becomes apparent after the commencement of a flight must be the subject of pilot judgement and good airmanship. The Commander may continue to make reference to and use of the MEL as appropriate."
Just because you've commenced the flight (i.e. taxi) then you just can't ignore a failure like anti skid, or engine failure and press on regardless!
The "commences flight" bit is to cope with a failure which can sensibly be carried - something like a pack failure say, which may be required to be wire locked closed under the MEL and placarded "INOP", but you may dispatch with just the QRH procedure (i.e. selected off) completed for your sector.