Great, well done! You ask for L Francis and manage to speak to them. Together, you speak with the counter staff at the Post Office. They distinctly remember somebody coming in to post a padded envelope. He was aloof when they asked what was in the package, was dressed unusually and all in black, and spoke with a thick Eastern European accent.
This was your spy for sure! A local postbox was out of service due to a lorry knocking it over, and it's this that may have forced him to use the Post Office.
The mail has already been collected and is on its way to London. You need a way to get to Mount Pleasant Mail Centre and you need to get there fast! You remember there's a Heliport somewhere nearby within 20 miles.
What's the name of the Heliport nearby? These emoji clues may help you.