Complex sentence: A second BBA&CER act allowed it to lease or sell itself to the MB&RR, and so in 1845 the two companies joined; the MB&RR later that year changing its name to become the East Lancashire Railway (ELR).
Split into simpler sentences: A second BBA&CER act allowed it to lease or sell itself to the MB&RR, and so in 1845 the two companies joined. The MB&RR later that year changed its name to the East Lancashire Railway (ELR).