You will have to walk to Border Control, wait for clearance, which could take some considerable time depending on which other flights have arrived with yours, then pass customs and into the hall landside, walk down to the far end, check in anything you do have ... remembering how tight FR are on hand baggage ... and then queue (for an unpredictable period) for security, access the lounge area and get to your gate which could be 20 mins walk away before the gate closes (theoretically) 30 mins or so before your flight is boarded (noting that this time limit is respected even if the incoming flight hasn't arrived on time, and you MAY find yourself doing the Stansted Stampede when FR changes their gate distribution at the last minute).
If you manage to complete this in your time plan, you'll be incredibly lucky. Wear comfy shoes and be prepared to run like the clappers!