Get yourself a nice strong piece of wire and attach it to the restrainer and its recepticle, open door gently and restrainer should come out, Mecano works nicely too!
Once you have the restrainer released, get yourself a suitable bolt with a plain shank on it, drop it down through the lugs on the door post and reassemble with a nut on the BOTTOM.
Don't forget to grease it all up nicely.
Now award yourself with your favourite tipple as Bob's your uncle, Fanny's your aunt and you shouldn't have had to go further than the garden shed!