On-street parking restrictions are generally worded as either “no stopping” or “no waiting”, rather than “no parking”. Yellow lines, for example, are a no waiting restriction, and apply to vehicles – your car is not allowed to wait where they apply, regardless of whether you are in or not, and whether or not the engine is running. Some restrictions, for example, the zig-zag markings outside schools, are “no stopping”, and even a very brief stop to drop off a passenger could result in a ticket from a camera. Being sat in the car also does not, by itself, prevent a penalty being issued.
It’s worth noting that although sat with the engine running is sufficiently “parked” for a parking penalty, it’s not sufficiently parked for the purpose of using a hand-held mobile phone, for which the engine does need to be off.