Decat or not?
 

Has anyone removed the catalytic converter from a standard exhaust system in the UK and managed to pass the mot?

You have a FD, it's helpful to put that in posts while in this section.
To answer your question, I would think passing ANY emissions test or visual inspection would be impossible w/o a cat.
Additionally the stench is pretty bad and there is some risk of boost creep on the stock turbos from too little back pressure. Worst case, that can cost you an engine.

im London based and let me tell you bro the emissions on a decat rx7 are the sole reason polar bears are drowning! You'll never pas the mot on a decat. Solution?

1) by a 1992 or early 93 model where they came out of factory without a cat so no need to be tested

2) fit decat and at mot time just fit the cat on for the test.

3) bribe the tester xD haha

i I done number 2 for many years until a found a friend who does mot and he was lenient on the emissions.