No. I think by law Sky have to pin protect any "adult" material, even if you are the only one in the house.
Found this on the Sky web site:
Unfortunately Sky are bound by an OFCOM regulation to force certain movies (i.e. 12, 15, 18) screened before their relevant watershed to ask for a pin number regardless of what the settings that a user has defined.So it depends when you view a particular movie on a channel and what rating that movie has as to whether it requires a pin at that time or not.
I agree it's rather mad but they're not currently allowed to remove the restriction.