2.0 zetec black top

[Big Vern]

On the contrary Baz,
Having spent 25 years working with the OEM systems to meet performance,economy and emissions targets set by legislation, the OEM systems are very complex and work closed loop at most of the operating conditions these days.
Autotune for the megasquirt system is pretty clunky and does not have any way of updating the VE and ignition tables properly while driving and the updating has to be saved and burned to the megasquirt memory. Not really the same system used by the major aftermarkets or OEM.
While it is true you are only tested at idle and 'fast idle' unless the system is mapped and runs the engine properly all the time the cat will be ruined by the time of the next MOT.
All this adds considerable cost which is way more than the cost of a cheap pre'95 zetec to get through the IVA with then you can put in what ever lump yo want - no cat reqd.
BV.