Does consumer unit (Wylex NN916) need to be replaced for electrician to sign off rewiring job?

You could always fit an RCD fusespur for the lighting circuit. Not the best solution, but it will do the job. Should save you a few quid too.

The Wylex NB type circuit breakers in the Wylex NN916 are obsolete and its likely that the unit has no RCD for electric shock protection. As such it would need to be upgraded or at the very least a second smaller consumer unit fitted that has an RCD in order for the lighting rewire to comply with BS7671:2008 and get signed off as safe and compliant.

It is down to your sparks interpretation but as I read it a damaged cable can be repaired or replaced in section for current cable colours and the only requirement by regs is to place a warning label at consumer unit of wiring using 2 different colours and is also not a notifiable job (counts as a like for like replacement). Leaving myself open for some prat to say you could replace an entire circuit and call it like for like replacement but we will always get those won't we. In saying that I would always recommend the fitting of a 17th edition board but that is down to the person footing the bill.