Looked on the virm and got this as a reason for rejection:
The exhaust system is so constructed that emitted heat
or fumes are likely to harm vehicle occupants, eg the
exhaust gases are not directed away from the perimeter
of the vehicle’s passenger compartment (Note 6).
Note 6 Externally venting wastegates (screamer pipes) are not permitted as they are not adequately muffled and the exhaust
gases passing through the wastegate are not directed through the vehicle’s exhaust system. However, wastegates that have
their own exhaust system or exhaust pipe exiting behind the passenger compartment are permitted
Question is...how far behind?