Assuming we are talking about Jersey Radar (happy to be corrected if not) then I believe it is SSR only. See
Replacement of Air Traffic Control Radar
19 August 2016
A 6-month project to remove the old primary radar and replace the secondary radar system along the Island's north coast is due to begin week commencing 22 August 2016. Although both primary and secondary radar systems are currently used by Jersey Airport the reliance on the former has decreased over the years and it also conflicts with the island's 4G mobile phone system. The decision has been taken to remove this primary radar and upgrade the secondary radar.
An aircraft could still be in the Designated Operational Coverage area (“in cover”) and not be ‘seen’ for several reasons. E.g. transponder switched off or unserviceable.