Complex sentence: Reports exist that suggest a degree of the disappointment with these locomotives was attributable to them being allocated to Class 7 work where they were only a Class 6 in reality; a problem put down to their very similar appearance to the BR Standard Class 7.
Split into simpler sentences: Reports exist that suggest a degree of the disappointment with these locomotives was attributable to them being allocated to Class 7 work where they were only a Class 6 in reality. A problem put down to their very similar appearance to the BR Standard Class 7.