I was told this evening by a retired signalman who worked Melton Constable that it was practice to send Call Attention before sending Train Entering Section on double track lines (although not on single lines). This is indeed as required by the M&GNJR double track AB regulations (March 1936 edition, reprinted May 1957) :
"Except in the case of the Section Clear or Junction Blocked signal and the Obstruction Danger sIgnal,and as otherwise provided for in Regulations 12 Clause (f), the Call Attention signal must always be given before any other signal and be acknowledged immediately on receipt."
Was this required anywhere else?