No the ECU is Ok, I had an in depth conversation about that with the nice people down the transport department.
The basic idea of legality with an mod is: you can't make any of the supporting systems, safety aids, emissions etc etc any worse than the factory specs.
Hence you can't replace an air-bag steering wheel with a lesser, non-airbag wheel.
In most cases an aftermarket ECU will improve emissions if tuned properly, getting rid of those nasty rich fuel curves!