James Bettley in the latest ("third") edition of Pevsner Suffolk East says of Halesworth Thoroughfare: "Further down, Nos 15-16 was built as a double guildhall by 1475, for the gilds of St John the Baptist on the one hand and St Loye and St Anthony on the other. Its exterior is now C18 and C19, with plastered and sashed front and a cornice decorated with quatrefoils. There would originally have been two open halls on the first floor, with a central entrance bay."

The Historic England listing is here with more detail and some interesting local reference sources.

Two views of the gilldhall follow:
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And from the other end:
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The extract(s) below are taken from one or more of the following articles in PSIAH (see the Sources page for details of how to access).

Morley, C., 1926, A check-list of the sacred buildings of Suffolk, to which are added Gilds. XIX Part 2, 168-211.

Redstone, V. B., 1904, Chapels, Chantries and Gilds in Suffolk. XII Part 1, 1-87. Has abstracts of 39 gild certificates, 18 in Bury (presumably the 1389 returns). Also details of Ipswich Corpus Christi gild.

Redstone, V. B., 1937. IV. Extracts from wills and other material, showing the history of Suffolk churches, chantries and guilds (Appendix to article published in Proceedings Vol XII). XXIII Part 1, 50-78.
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For information on buildings mentioned in the Pevsner guide to Suffolk in this location see pevsnersuffolk.co.uk