Electrical sub-contractors are in the invidious position of having a legal requirement to sign off on their own work with the added onus of their declaration of completion being simultaneously a safety certification. This makes them naturally loath to do so until as late as possible, especially if their contracted segment is part of a complex integration with other contractors' segments, be it electrical, IT or safety systems (in this build there are several other segments too, given that the stadium functions also as an industrial brewery, entertainment complex, leisure centre and various other ancillary roles normally restricted to dedicated structural projects but in this case combined).
The main contractor can tackle this in two ways - either insist on each segment being "passed" by the sub-contractor at point of completion, or employ an intermediary electrical contractor to assume separate responsibility for the integration as each segment completes and then pass these at each point along the way, an approach that makes it easier for the final arbiter of safety, the council, to pass the entire build in one go but which also has huge potential for cumulative small delays along the way as well as higher costs as the sub-contractor's role does not complete until the third part says so. In this case, because of the time constraint, a "middle road" seems to have been pursued in which some sub-contractors' work was deemed complete and safe based on their unilateral declaration while others working on more critical systems awaited integrational testing prior to being released, the risk taken therefore being that a previously "passed" system, not originally considered as high-priority in relation to safety, is deemed ultimately unsafe when viewed as part of the integrated whole and prevents other "passed" systems, even ones of critical priority, to be cleared until the lesser system is also addressed. They seem to have taken this risk and lucked out. The main contractor in this case, anticipating the BCO, has declared itself dissatisfied with the level of integration at this point of the project and insisted on more time, previously unanticipated, to address this.
If this wasn't a football club's stadium, in which so much more is at stake commercially regarding perceptions of performance -often held and expressed by absolute ignoramuses when it comes to construction and what this entails - then it would amount to a slightly embarrassing delay while some company moves into its new headquarters or similar, a very normal occurrence (in fact an absolute norm when it comes to big builds). Unfortunately for Spurs, and Mace, it's being played out under very public scrutiny by a public who are inclined to see a word such as "safety" in press releases and immediately assume sprinkler systems or who see any apparent void in the external fabric of a building under construction as a logistical lapse and evidence of "over-run".