There’s some legislation that mentions ‘rally car or extensively modified’ that does allow you to remove certain factory fitted options. So if you had a rollcage, harnesses and removed back seats etc then you should be ok, but it’s a little grey and not all testers would pass your van based on these regs.
Also your insurance company would not be happy about it unless you specifically told them.
People with track slag, but road going E36’s or Jap drifters would most likely get way with it because they are so heavily modified.