JCT SBC Without Quants contract but client wants to add D&B variation

We are currently delivering a job under SBCC xoQ 2016 and the client wants to add additional work into our scope but on a design and build basis. If we agree to this work, does this affect the contract as a whole in terms of us having to take on the design responsibility?

The Contract contains CDP elements and as long as these are completed properly then this should not cause any problems. You need to make it clear that taking responsibility for the CDP elements does not mean that you take overall responsibility for design.