The following text is from the original listed building designation:
1. 5275 CHURCH STREET ST MARY'S (East Side)
Boundary walling to the rear of Nos 16, 18 & 20 TR 3258 1/245A
II GV
2. Mediaeval stone and flint boundary walling at the rear of Nos 16, 18 and 20 approximate height 7 ft by a total length of 130 ft on 3 sides. Nos 16 to 22 (even), Walling to rear of Nos 16, 18 and 20 Nos 26 to 34 (even) and walling between Nos 32 and 34 form a group.
Listing NGR: TR3292558350
(1)

The wall was delisted in 2013 as it was found to be of 18th century date, not medieval.

From the delisting report:
Details
DATE: the end garden wall forming a boundary between Nos. 16-20, Church Street and Nos. 13-17, Bowling Street is probably C18 and the wall forming the south-east side garden wall to No. 16, Church Street is early C19.

MATERIALS: the end wall is mainly constructed of brick, either yellow or red, but the south-east side garden wall to No. 16 is mainly constructed of flint, knapped and unknapped, with a brick parapet.

DESCRIPTION: the end garden wall of 16-20, Church Street is approximately seven feet high and 39 feet long and is constructed mainly of yellow brick but some red bricks in a fairly random bond pattern. Much of it is in header bond and has a C19 brown brick coping.

This wall faces directly on to the end gardens of Nos. 13, 15 and 17, Bowling Street which has a wall directly abutting the end wall of Nos. 16-20, Church Street. This wall is also about seven feet in height, is a mixture of red and yellow bricks, partly in English bond, partly fairly random bond. There is a parapet of bricks on edge. An iron tie is present in the section at the end of the garden of 15, Bowling Street but part of the wall had collapsed at the time of inspection.

The south-east side garden boundary wall to No. 16, Church Street is a lower wall mainly constructed of unknapped flints with a few pieces of reused masonry and has a parapet of two courses of yellow bricks. (2)

<1> English Heritage, List of Buildings of Special Architectural or Historic Interest (Map). SKE16160.

<2> English Heritage, 2013, English Heritage (Listing) Advice Report Boundary wall to the rear of 16, 18 and 20 Church Street St. Mary's (Unpublished document). SKE25999.