You can fit LED bulbs in the Seat fog lights but they must be the correct type.
LED fog light bulbs that have LEDs distributed around a cylinder, and also have front facing LEDs are projector bulbs. These are for projector fog lights, in which the front glass is a lens that shapes the beam. If they are fitted to a Leon fog light they will scatter light in all directions.
Leon fog lights have a plain front glass and the beam is shaped by the reflector/halogen bulb combination. The relatively small filament of the bulb is positioned as a single source of light at the focal point of the reflector. This produces a controlled wide beam with a sharp horizontal cutoff. Also, the bulb is capped to prevent uncontrolled light from being projected forward to obliterate the cutoff and dazzle oncoming drivers.
A replacement LED bulb must have an LED, the same size as the bulb filament, attached to each side of a flat blade. The blade must be vertical when installed in the housing and must be capped.
Two reliable brands offering the correct bulbs are Nighteye and Novsight. I fitted Novsight bulbs from Amazon. When I fitted the first one the cutoff aligned correctly with the original bulb in the other fog light. A scan with
OBDeleven showed no fault codes. The beam from a fog light should decline from the horizontal by approximately 3 degrees.
The images in the Amazon listing show the structure of the bulb. They are cheaper on Ebay but Amazon is a safer bet because you can return them if you experience any problems. There are very similar bulbs on ebay that are not capped. They are projector bulbs.
https://www.amazon.co.uk/NOVSIGHT-H...8451271&sr=8-1&keywords=novsight+h8+fog+light