I looked up Dunstable Downs and it looks absolutely NOT suitable for jump suicides. Please don't do this. You will likely survive and end up permanently disabled in various possible ways. You could end up trapping a leg or arm between the wheels when you land and tumble, then those limbs will break and twist and someone finding you will get you medical "help" and they will amputate those limbs because they are unsalvageable. You could land on the face on your bike and break all your teeth and lose an eye from some part of the bike piercing it. I've seen many videos of failed suicides to know that the body can endure a lot and still be alive. And those cliffs are nowhere near the height required for a jump to death, even if they were towers. PLEASE research other methods.