Attempting a broadcast with an intermittent power supply is extremely difficult. On the one hand you have mains electricity some of the time and can work normally preparing as much as you can should the worst happen ... and then you have a power dip or momentary cut and it's enough to lose lots of data, send technical equipment into lengthy boot-up routines and even kill sensitive bits of kit that rarely gets turned off. It's unpredictable and hard to plan for.
Often due to the high power demands of TV studios, UPS will maintain only select bits of the set up to get a simple programme on air - one camera, some low energy lights (soft studio flourescent fill lamps can provide enough light for modern cameras at less than 100W: a single tungsten key lamp can be 1kW at the least), an autocue hood and PC, a small gallery, maybe one edit suite for playout. If you need to plan to move a programme as complex as News at Ten into a studio with only limited kit it's a tall order to say the least in terms of planning, let alone logistics,
I am sure there will be a steward's enquiry into this incident, but the programme looked perfectly acceptable and as far as a Broadcasting Contingency exercise goes, was a triumph.
Two minutes regions...