Sections 164 & 165 of the Road Traffic Act 1988 make it an offence (maximum fine £1000) to not instantly produce driving licence, MOT and/or insurance certificate at the roadside if requested to do so by a constable. However, you cannot be convicted of the offence if you produce said documents at a police station within 7 days - the HORT/1 is the means by which you can nullify the charge of "failing to produce..."
This is separate to a charge of "using with no insurance" (maximum fine £5000, 6-8 points or disqualification). The HORT/1 also allows you the opportunity to supply documents to defend against this charge and failure to do this (whether or not it is marked on the HORT/1) does not stop the original constable from commencing a prosecution when he receives the HORT/2 from your nominated police station, assuming they do not spot the obvious discrepency.