Complex sentence: After the failure of the InterCity 250 project to gain Treasury support, British Rail ordered a small number of Class 91 locomotives, but the manufacture of Networker rolling stock at the time precluded these being built.
Split into simpler sentences: After the failure of the InterCity 250 project to gain Treasury support, British Rail ordered a small number of Class 91 locomotives. However, the manufacture of the Networker Rolling Stock at the time precluded these being built.