Peter Smith asks this question on SpendMatters Europe today.
My view is that neither the Directive nor the Public Contracts Regulations 2015 impose a definitive obligation of dividing a procurement process into lots.
Article 46(1) of the Directive states that contracting authorities may use lots. If a direct command was meant the appropriate word to use would have been shall and not may. Article 46(4) however authorises Member States to actually mandate the use of lots.
However, that implies that in the transposition the appropriate mechanisms/pieces of legislation are put in place. As I have mentioned many times before, Central Government decided to pretty much copy and paste the Directive, and that option was not taken up. Furthermore, In addition, the second paragraph of Article 46(1) of the Directive expresses the obligation of the contracting authority to explain why no lots were used when the division is not mandatory. In other words, if the Member State does not make the division into lots mandatory, then contracting authorities must provide reasons why they have not done so. Explaining the decision is the extent of their obligation.
As for the PCR2015, Regulation 46 maintains an identical approach to that of the Directive. Paragraph 1 mentions that contracting authorities may use lots and paragraph 2 that there is a need for the decision by the contracting authority to be explained ("an indication of the main reasons").
That is all that is needed.