Complex sentence: Later the Coventry Canal company bought back the northern (T&M) section, but since the middle section remained part of the Birmingham and Fazely Canal, the northern section is nowadays referred to as "Coventry Canal (detached portion)".
Split into simpler sentences: Later the Coventry Canal company bought back the section built by the T&M company, but the middle section remained part of the Birmingham and Fazely Canal. The T&M section is nowadays referred to as "Coventry Canal (detached portion)".