Might be worth checking what the MOT rules are?
Is it the physical existence of a cat, or just the emmisons?.... because it might actually still pass without one.
Just emissions as far as I know.. Some cars will pass without no problem.. Civic Type R's always did..
Thought as much, most do as far as I've heard, so long as the mapping is corrected properly to deal with it
Perhaps you could request Revo write a map that drops the emissions low enough sans-cat to pass an MoT? Loading an 'emissions test' map would be a lot easier than having to replace the cat every year.
I'm not sure who offers the choice of using the cruise stalk to change between maps (GIAC?) but you could one step further and have the emissions test map preloaded on the ECU. Then, on the off chance you ever get pulled for a road side test, at the flick of a switch, you'd pass and be on your way (will just a retification order for a defective - read: too noisey - exhaust).