Sparky
Consider the following.
Examine the other front door to see what the normal action should be. You will see a "star" wheel on the door. This engages with the short "rack" mounted on the B pillar. When you open the door by either pressing the external button or using the interior handle, the "star" wheel is released and can spin freely. Then a gentle pull from the outside or a gentle push from the inside will open the door. When the external button or internal handle is released, the "star" wheel re-engages and will not spin freely.
Your problem seems to be that the push button or interior handle (or both) are not releasing the "star" wheel.
First thing to try is to move the interior handle through its complete range of motion (from "closed" to "lock" to "closed" to "open" several times. This to determine if a sticky mechanism can be convinced to work by jiggling it several times.
If that doesn't work, with the door unlocked have someone hold the exterior button in while you hold the interior handle to "open". Then put your shoulder into it, ie using (gentle) brute force to to try to force the door to open.
For details of the front doors refer to section S2 of the Workshop Manual (available from
www.rrtechnical.info ).
Once the door has been opened you will probably need to determine why it got stuck and fix it.
Good Luck.
Leho