The computer systems are linked now, only problem is if there are any oustanding fines etc, you have to go back to the tax office to pay them first, so unless you are confident that there is nothing outstanding you can go straight to the mot centre(you should know if you have recently paid your tax, any "extras" would have shown up then). Another thing is that the emmisions test has to be done before you get there, and I was told when I went to the Fiat garage that they didn't do them and they sent me to the Nissan garage down the road (I have a Fiat).