Guys,

I am kinda going crazy here. The Service Engine Light came on, and a friend with a machine came and hooked it up, and it said Gas Fume Leak (LARGE). However, we thought I may have left the gas tank lid loose. He turned off the service light.

A few days later, I go fuel up, the gas light turns on again, now I am smelling a bit of gas fume inside the car.

Where can I even get started with this?

 

This is one of those examples of where writing down the numeric code would help, some readers have different text than what the Rover manual has. But a large leak (code 455) is one beyond a certain pressure level, and expected size, so this one should exceed 1 mm. Usually the gas cap or loose hose. Here's plan from RAVE on the evaporative system, and a second page on the fuel tank coponents, I'd start at the gas cap and work along the system looking for a loose clamp and certainly signs of leaking fuel. Check gas cap. Do this outside, no point burning down the garage. If you are not DIY mechanical, print these pages out and take them with you to an indy shop.