So imagine this:
Your rad explodes (not impossible)
Ensuing panic means you spin into the armco
Car is a write off (£7K)
Armco damaged (£4K guess)
GT3 behind you hits your coolant and spins into the armco
GT3 is a write off (£70K & armco £4K)
GT3 clips a biker, writes off his bike (£8K)
Biker needs air ambulance and is crippled for life (£500,000)
Value of £600,000, ish. Just for a quick 10 min lap of the Ring. Massively unlikely to happen, but it's at your own risk.
Or you could do a trackday out there, get the whole use of the straight and insure yourself up for about £1000. Bargain, I reckon.