The interesting thing with the boot release is that I'm sure it says in the manual that the release will only work at speeds below 4mph

However, as has already been said it only works with the engine off and the doors unlocked.
My wife's 1995 1.6Si boot release also only works when the engine is off, so it looks like that's normal for Ford.
The boot release on the key does need a double press. I think this is to stop you opening it by accident. It was exactly the same on a Modeo I had 3 years ago.
I've got my central locking set so that on one press of the the unlock button it only opens the drivers door, needs 2 presses to open both. Most of the time there is only me in the car so I prefer it this way.