Members of the Civil Defence General Services that had been trained by the St. John Ambulance Association in first aid could wear an embroidered badge on their battledress blouse or tunic. These badges had "St. John Ambulance Association" around the circumference with the Royal Order of St. John's Amalfi Cross at the centre (the lions and unicorns had been granted by royal patronage).
Founded in 1877, the St. John Ambulance Association was created to provide first aid training. The St. John Ambulance Brigade was founded in 1887 to provide uniformed medics at public events. The two were merged in 1968.
The below yellow St. John Ambulance Brigade celluloid pin badge has ARP in the centre. I've not come across any documentation specifically about this badge but I presume it was an early war badge for wear on civilian clothes by members of the brigade who were also volunteering within the ARP services.
Examples are quite scarce and prices can be high for the badge (£30+).
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