I've just done one this evening, and it took less than 10 minutes.......admittedly the arm was off already, and the centre belted out.
So, if the bolt securing the upper arm is seized, chop through the bolt ends, then belt the centre of the bush out with a mash hammer.
Or simply use a selection of spanners like this
This should do the actual job,
LINK I can't be bothered to trawl for the picture of the Vectra rose joint bush tool that I machined up a different cup to accommodate the deeper body of the R40 bush.
But this is the thing in question
My advice is to use a rotary wire brush to clean the part of the trailing arm that the bush is fitted, before attempting to draw it out.
Also make sure the thread of the tool is well greased before you start ;
Have fun
Brian
P.S. the Vectra bushes look like this
P.P.S you don't need to remove the arm from the car, nor do you need to use a 20 ton press