can a cat flap be put in a double glazed door ?

YES A CATFLAP CAN BE PUT IN A DOUBLEGLAZED DOOR ,BUT ONLY IF THE DOUBLEGLAZED UNIT IS CHANGED TO ONE WITH PRECUT HOLE IN IT.FOR A CATFLAP.AS MOST D/G UNITS ARE TOUGHENED GLASS AND WOULD DISINTERGRATE IF CUT. YOURS G.H.M

Yes, you will need a new sealed unit with a hole cut in it.

i have seen them in where the glass is in top half and upvc bottom half, but i wouldnt have thought so in a all glass door as im led to beleve the glass is a sealed unit and to cut glass would break the seal, your best be would be find a double glazing tradesman of this site and ask him direct. he may also have another way around the problem.