How do I remove a derivative rule using remrule?

Hi,

I have no problems using remrule to remove rules attached to functions
or operators such as "+", but I can't work out how to use it to remove
rules attached to derivatives. Nothing I try seems to work:

(%i1) tellsimpafter('diff(xx(t),t,1),dt(xx));
(%o1)                    [derivativerule1, simpderiv]
(%i2) rules;
(%o2)                          [derivativerule1]
(%i3) remrule(derivative,derivativerule1);

remrule: no such rule: derivativerule1
 -- an error. To debug this try: debugmode(true);
(%i4) remrule(diff,derivativerule1);

remrule: no such rule: derivativerule1
 -- an error. To debug this try: debugmode(true);
(%i5) remrule(simpderiv,derivativerule1);

remrule: no such rule: derivativerule1
 -- an error. To debug this try: debugmode(true);
(%i6) rules;
(%o6)                          [derivativerule1]

Can anyone enlighten me?

Thanks,

Bernard.