Can we invite the bidders who responded to a PIN to take part in a competitive process or do we need to readvertise the contract?

We sent out a PIN early January to test the market. Several companies replied or requested more information and 5 companies submitted expressions of interest (EOIs) and met all the criteria set (all major, national players). Our procurement department now tell us that we have to go back out through an OJEU Open Tender process which would take about 4 months. Following the EOIs, we would want to invite all 5 companies in and put them through a competitive process instead of readvertising via OJEU. Do the new 2015 procurement regulations allow us to do this (i.e. use the PIN instead)? The value of the procurement will be well above the OJEU thresholds.