It's unclear to me whether you are intending to comply with EU MDR or only UK regulations, but from an EU MDR perspective - you need the lot number because the device must be labeled with the complete UDI in both human readable and AIDC format. The UDI consists of the DI (device identifier, eg GTIN) and the PI (production identifier, eg serial or lot number).
UK MDR 2002 also requires the LOT number to be labeled on the product, where appropriate. So even if you were following UKCA you are still not meeting the requirement. It sounds like there is a lot going on in this situation so IMO, the label is only one of several worries here for you.
Realistically, you may or may not get caught by the CA. If it is a class I low risk device...they may not waste their time. However, risk level and consequences should not be the reason you don't fix your situation here.