Underbody reinforcement

As I said in my first response and backed up by others this steel pressing is to help stiffen the bodyshell. MG Rover found that the MGF needed stiffening even more and the TF included extra braces under the spare wheel well, the dashboard braces and the above engine braces. MG Rover would not have added extra stiffening if it was not needed, however if you just potter around then as I said it may not make a noticeable  difference.
Until I get another "run around" car we are using the TF to take garden rubbish to the tip and despite it being smaller than my old Fabia estate I can get almost as many bags in the boot! It never bottoms out on the speed bumps that our other car scrapes the under body on, the TF never touches them. It must be a problem to some though because someone else asked the same question about removing the reinforcing panel on another forum a few weeks ago.

Solved!!
4 mm galvanized iron was the solution. 
I applied 3 coats of mate black to protect and now I can get into the garage without problems!!


 

You have done well fabricating this panel.  How much difference does it make to the ground clearance in centimeters?

I’m quite taken with that idea, I’m shortly going to fit lowering suspension knuckles * & like you I’ve a hump to overcome as I reverse into the garage.
I could go under the car & measure the gain by fitting a plate but we’re off for a week away.
*the fitting of the suspension knuckles has been threatened for the past few years. They’ll need another coat of paint by the time I’m ready.
M

Between 3 and 5 cm, which does not seem like much, but for the ventral angle it is a whole world.
For me, it's a great solution. 

30 to 50mm is a useful gain!