Complex sentence: They were so popular with the ex-Great Western crews that the British Railways Western Region operating authorities wanted more of the class built after nationalisation in 1948; however, this request was turned down in favour of BR Standard Class 9Fs.
Split into simpler sentences: They were so popular with the ex-Great Western crews that the British Railways Western Region operating authorities wanted more of the class built after the 1948 nationalisation. However, this request was turned down in favour of BR Standard Class 9Fs.