The obvious word would be summoner . But be careful. Though no such named office exists in the British judicial system, the name used to be that of an officer in English medieval ecclesiastical courts.
Indeed one of Chaucer's pilgrims was a Summoner. A modern prose rendering of the Prologue notes the office of the Summoner as:
An officer or constable whose task was to summon delinquents to appear
before ecclesiastical courts, enforce payment of tithes and church
dues etc. He also had power to punish adultery, fornication, and other
sins not punishable by common law. The Friar's Tale is a satire on
the abuses practised by Summoners.
Chaucer describes his Summoner in the Prologue as having:
...slit eyes and a flaming red visage like a cherub's, all covered with
pimples. He was as randy and lecherous as a sparrow. Children were
afraid of his face with its scabbed black eyebrows and scraggy beard.
No mercury, white lead, sulphur, borax, ceruse, cream of tartar, or
other ointments that cleanse and burn could rid him of his white
pustules or the pimply knobs on his cheeks. He had a great love of
garlic, onions, and leeks, and of drinking strong wine red as blood,
which made him roar and gabble like a madman. When really drunk on
wine he's speak nothing but Latin...He was a tolerant, easy-going dog,
as good a fellow as you might hope to find. For a quart of wine he'd
allow any rascal of a priest to keep his concubine for a twelvemonth
and excuse him altogether; however he was well able to fleece a
greenhorn on the sly...
David Wright: Modern prose rendering of Canterbury Tales by Geoffrey Chaucer.