40 minutes is not nearly enough time to connect to any flight from T-A to T-C at EWR, especially international. Also, alot rides on when the IAD-EWR segment is scheduled. If it's the first flight out in the morning, it will go on time...but if it leaves at 5pm, count on at least 1 hour of delays due to ground stops at EWR...more if the weather or winds are iffy. I am assuming this is an evening departure to LGW, so your IAD flight might be the 5pm, unless you can switch to the 3pm. The 5pm departures from IAD and DCA are notorious for 45-90 minute delays, sometimes more if the weather is bad.

Try to take the 3pm flight, buy a couple passes into the PClub and relax...your blood pressure will thank you.

Assuming the flight arrives on time, 1 hour is a minimal number for an inter terminal connection.

When you arrive at T-C, the Airtrain will dump you in front of the main security checkpoint. If it's busy, immediately head upstairs and walk to the far end of the terminal where the stairs lead down to the checkpoint for the 12x gates (new concourse) and try the checkpoint there...it's usually much, much less crowded, and your flight will probably depart from there anyway. The brain dead ID checker might try and force you to another checkpoint if your flight leaves from the 70s, just hold your ground and insist you're going to the Presidents Club and have every right to use whichever checkpoint you want.