unwiseowl & dhc83driver,
The 'spy in the cab' doesn't record fast taxy speeds.
Taxying without the flaps set to atleast 18 degrees isn't a SESMA so long as the wheel speed is less than 7 knotts. If this was the case every time you were pulled forward by a tug you'd achieve another event.
The reason we use a standing start for all take-offs when within 2 tons of RTOW is to account for differences in piloting technique on performance critical take-offs. BACX in all its wisedom has come up with a blanket rule to cover for the lowest common denominator, therefore, all BACX RJs departing LCY have to perform standing starts. In reality, the performance allows for rolling starts at LCY.