As it happens they will, if you subscribe to network services (Call Barring). They used to try blocking Mercury 131 as well, when a caller used Call Barring, but that nice Mr Oftel had a word with them about it...
For payphone lines, BT add a (very annoying) tone for the first minute of incoming calls, to indicate to the operator that this line is not to accept reverse harge calls.
I am not sure of the details, but am fairly certain this is an option you can ask for, just tell them you have a private payphone on the line. You may have to pay for it, possibly combined with meter pulsing.
Phoning one of these numbers now requires use of a PIN (personal identification number) from your telephone, and they will only provide you with such a number if you ask for one. This number will only be required on the 0898 Premium rate numbers.