D&B tender evaluation: lowest price vs ER compliance

Your practice is appointed as Employer's Agent on a £8m mixed-use scheme in Bristol: 38 apartments above 1,200 sqm of ground-floor retail. The procurement route is JCT Design and Build 2024 with bespoke amendments drafted by the employer's solicitor. The client is a private regional developer. Your practice also took the design through to RIBA Stage 3 under a separate RIBA Standard PSC 2020 appointment, and the appointment provides for novation to the successful main contractor on contract execution using the CIC Novation Agreement 2018. You have therefore worn two hats, designer (pre-novation) and Employer's Agent (post-novation), with the consent of all parties. Three D&B contractors have tendered against the Employer's Requirements. The two higher tenders are £6.78m and £6.84m and are fully compliant with the ER, including the specified fully unitised aluminium rainscreen cladding system with A2-s1,d0 mineral wool insulation. The lowest tender is £6.33m, £450k below the next bidder. The lowest bidder has substituted an alternative through-coloured render system on a ventilated rail support with PIR insulation, claiming compliance with Approved Document B by reference to a BBA certificate. The Contractor's Proposals also include a programme four weeks faster than the ER milestone schedule and an alternative drainage strategy that omits the rainwater attenuation tank required by the lead local flood authority planning condition. The client's finance director has telephoned you and said that the £450k saving is decisive and that the client wants to accept the lowest tender today, ahead of a board meeting tomorrow. The client adds, as if helpfully, that since you are about to be novated to whichever contractor wins, you will be running the technical design with that contractor anyway.