The following is based on my experience arriving on a domestic flight at Stansted in early April 2018:
If you have baggage to claim, you will have to re-enter the departures area through security like a normal passenger. There's only a single domestic baggage reclaim belt at Stansted and certainly no special transit corridor or similar.
However, domestic arrivals are routed through the departure lounge at Stansted, so if you had only hand luggage, you could simply head to the gate for your connecting flight, making sure to leave plenty of time in case your boarding pass not having been scanned at security poses an issue. Note that many airlines reserve the right to check your hand luggage, so I wouldn't rely on this to make a tight connection.