WWII Seafire wing webb
Here we have a part from a Seafire III which was the naval version of the Spitfire and basically similar to a MK V Spitfire although it was fitted with a Merlin 55 and had folding wings with an arrester hook for carrier landings
This is marked 358 08 sht 41 and appears to be an internal frame located near the wheel well as it has a section designed to take the undercarriage leg when retracted. This is quite a heavy duty item and appears to be a main support.
The attached photo shows a similar item as fitted to a MK IX Spitfire. It can be seen to the bottom right of the picture but it is a more substantial item, being fitted to a Seafire, for extra strength.