Sorry to be so vague.
Since you offer no clarification here - I'll make my own assumptions.
You're inserting a plane in your part.
YES
This plane needs to be at an angle to another plane.
NO, I WANT IT PARALLEL
You insert this new plane, using an existing plane and an axis or an edge.
YES, A MAJOR PLANE IN THE ORIGINAL SW MODEL AND AN AXIS (HOLE CTRLINE)
The default angle is 45 degrees.
WHY IS IT DEFAULT AT 45 INSTEAD OF ZERO?
Simply type-in a new angle.
YER RIGHT THAT IS QUITE SIMPLE BUT I AM WAY SIMPLE MINDED AND DID IT NOT USED TO BE DEFAULT AT ZERO?
If all else fails- double-click the new plane in your feature manager and edit the angle dimension that pops-up on your model.
YES THAT WOULD WORK TOO. JUST DON'T WANT TO BE BOTHERED CHANGING WHEN MOST OF THE TIME ONE USES PARALLEL PLANES.
IS THERE A WAY TO FIX IT?