So your door does not stay in the lock. Lock Mechanism 914695

 So after fixing the door handle some time ago:
http://triumphspitfireiv.blogspot.com/2021/01/520260-520261-triumph-spitfire-control.html
http://triumphspitfireiv.blogspot.com/2021/01/door-lock.html
http://triumphspitfireiv.blogspot.com/2020/12/door-lock-mechanism-cleanup.html

I wanted to mount the door latch (lock mechanism 914695)
But the door would not stay in it's lock...

On the passenger side the lock mechanism was working just fine....

So after some work on the Lock itself i found that the Spring was broken:

Grind the little pin on the back of the lock

And on the front of the lock

Then you can open it and see how the lock works.

Testing with the new spring:

Without the outer plate:

Now the door has a good lock!