SEC'T = 'secret' . Probably used with a GPO/PO 'extension Plan 12A' which had two phones in parallel on the same line with the facility to 'switch' one of the phones off the line to afford secrecy for the other - plus the ability to call between each other. See
https://britishtelephones.com/extnplan.htm under Plan 12 and 12A.
'Recall' was originally used on Private Manual Branch eXchanges to recall the operator. Flashing the switchhooks which was done on a call to a public manual exchange could not be used on a PMBX exchange line call as both operators would respond! On a Private Automatic Branch exchange, it was used on an outside call to return internal dialling tone so that the call could be transferred. On earlier PABXs, it used a system called 'earth recall' which needed a separate earth wire to each telephone but in the 1980's 'Timed Break Recall' (effectively the same as dialling '1' with a pulse dial) replaced 'earth recall' BT referred to 'timed break recall' as 'Register Recall' - hrence we have the Tone Dialling Telephone 782R with Earth Recall fitted and the Telephone 782RR with 'register recall' fitted (a separate PCB inside the phone). The Tele 782RR is a lot less common than the 782R.