Illustrator script runs slow when called from menu

I have a script that I've placed in Presets\en_GB\Scripts for testing purposes so it appears in the File > Scripts menu.

The script in question calls another script as part of the process, when I run the script from File > Scripts it makes Illustartor hang for about 10 mins whilst its running, the script completes what its meant to do all ok.

I run the exact same script but as an action using 'Insert Menu Item', to call the script from the File > Scripts menu, when I do this it runs the same process but in about 30 secs.

I have no idea why this is, what is it about running scripts via the actions panel that makes it so quick. Even though this method works, I really need to get it working from the File > Scripts menu.