Depends on what the dealer or previous owner or garage has done.
Mine (04 plate) were held on by double-sided tape.
The answer is no by the way. 3M or Halfords double sided tape been recommended on here by others previously.
Mine had personalised plates previously so the stock plates were put back on by the tape. This is of course if the plates aren't stuck onto the backing plastic plate or car by screws
Though the previous plates were stuck on using normal thickness tape, I was a little concerned like you, and as the front bumper is curved (not straight plane), I got pads from Halfords to accommodate the curve. There were two thicknesses and the thinner one (about 3mm I think) worked a treat. I can't find them on the site. There were a few quid. Hang on I also bought some thicker ones so I might have them knocking around at home. I can have a look in the next couple of days if not a rush?
Like Oakandacorns said it all depends on the previous owner / dealer put them on with.
Mine were screwed on and when I fitted the M bumper on the front I tried to stick the new plate on with doubled sided number plate from Halfrauds but due to the curvature of the bumper (I decided to do away with the plate holder) it kept pulling away so ended putting in 2 screws.
When the new rear goes on the tape should hold as it's flat.