Seems you have not yet had any help, so maybe my 147 experience might help if they are similar.
I have a row of allen headed screws visible when the boot lid is opened. At either side there are a few more visible from underneath (long reach extension required to reach them)
In the wheel arches there is a flexible inner cover which can be eased back to get access to two or three more screws, usually under a lot of mud.
I undid all except the middle ones in the boot before getting help to hold bumper and unclip the number plate wiring.
A) You have to remove the 4 torx screws that are hidden by the boot lid.
B) Remove the luggage compartment side trim to get at 2 more torx screws on each side
C) Remove two phillips drive screws from the wheelarch
D) Remove a couple of Torx screws securing the bumper to the sparewheel well.
I cant remember if there's also a couple of screws securing the lower part of the bumper to the rearwheel inner lining.
Oh, and also: make sure you remove the licence plate lights and undo the bulb holders.
There are some seriously misleading instructions around on removing the rear bumper. To be generous it could be that early cars - pre 05 facelift are completely different ... but.. having just done it on my 56 reg Ti.. here is the real gen:-
1. Remove 4 off Torx screws along the line hidden by the rear door edge - very obvious T30 is the size with an M6 thread.
2. Remove the 2 self tappers into clips that hold the wheelarch trim - one at bottom corner one at the top.
3. Push the wheelarch trim - tough cardboard - to one side to access two per side of the same Torx screws as in the boot edge. Need a long driver coming from below one at front corner one right back.
4. Take out hree more similar Torx along the bottom edge onto the spare wheel well
4. Then slide out bumper unclipping plug for parking sensors (if fitted) and twist to remove number plate bulbs.
I made the mistake of following instructions elsewhere on this forum to access Torx by removing internal trim.. not necessary!!!
Not entirely certain why you decided to revive a 5 year old thread :lol: - but there are 3 torx each side of the boot aperture going down into the bumper, and as you indicate one at the front each side coming up from below - which can be a real pita to get at without removing the arch liner......
I tend to think 15 minutes is a bit optimistic for a first attempt......
It took me two hours - partly stripping out the inside of the boot to find the mythical bolts.
15 minutes is to do it again knowing where everything lives and which tools get to them!!!
Just for reference my bumper has two Torx each side going up behind the arch liner.
Thread was revived because it is still useful and earlier instructions were what had me stripping out the boot trim.