The aisle is only slightly later than the nave and chancel, probably dating from about 1200 when the Norman style was giving way to Early English. Between the aisle and the nave is an arcade of four arches though only three of them are contemporary with the aisle; the fourth (the westernmost one) dates only from the time of the Victorian restoration, there having previously been a plain wall there. Aisles, generally added to accommodate growing congregations, were most often built first on the north side (the devil’s side) of the nave to maximise burial space on the south (or God’s) side and avoid having to rebuild the porch. A reason for departure from this custom at Englefield may be found in the lie of the ground, which rises quite steeply on the north side.
The current porch is therefore at least the third to have been built at Englefield for Tomkins shows an earlier one and there would have been another, leading into the nave, before the aisle was built. The porch was an important place in the Middle Ages, for both secular and religious purposes. Here oaths were sworn, bargains struck and disputes settled but here too were performed marriage ceremonies (for the lower orders) and the initial part of the baptism rite. The main entrance to the church is by this south doorway into the aisle and the header is original, though the rest is heavily restored.
The font is always a prominent feature at the west end of a church close to the entrance, though if the aisle did indeed not extend as far back as it does today the font at Englefield must have formerly have been in a different place. Indeed it must have been originally in the chancel anyway, since the aisle is a later addition.
The east window is a notably fine example from the 13th century, though the stained glass in it with its depictions of the twelve Apostles (Matthias replacing Judas) and St Paul dates from about 1850 and is by John Hardman of Birmingham. Ashmole describes the glass in this window as having two shields of arms on it. The south and west windows certainly date from the Victorian restoration in their entirety and we can see on the inside how these had to be fitted around the monument to Mary Benyon and the doorway. The south windows formerly had three shields of arms on them, one the arms of the Englefields. Plain glass was installed in 1967.
Close to the northern side of the east window is a 13th century corbel or bracket, possibly intended to carry a devotional statue, and next to it is a hagioscope or squint, assumed to have been blocked when the chancel was rebuilt in 1855. Traditionally the purpose of the squint was to enable a chantry priest at a subsidiary chantry altar to follow the actions of the principal celebrant at the high altar. This suggests that there was originally a secondary altar in the aisle, as there is today, this one being the one displaced from the sanctuary in 1891 and which the reredos was designed to match. We therefore suppose that the aisle might originally have built not merely to increase the number of people that could be accommodated in church but also to house the chapel of the Englefield chantry of St Mary, known to be in existence before 1386. If that was the case then the altar would probably have been situated under the bracket where the radiator is today for the alignment of the squint is such that only from that position would the Chantry priest have been able to see the priest in front of the main altar. The bracket probably carried a devotional statue of the Virgin as patron Saint of the Chantry. At the point where the hood moulding of the eastern arch meets that of the next one along is a carved head, although it is now quite literally de-faced. This is the only one of the four such intersections that has this feature so it may well be further indication that this part of the aisle had some special significance.
In the south wall are two modern arched niches, each containing an early effigy. These are now somewhat obscured by the Victorian seating but Tomkins drew them, presumably at the same time as he drew the outside of the church and before the new seats were installed. W Fletcher in his 1841 book A Tour Round Reading described the effigies.
Fletcher supposed that the male one was meant “to represent Alwin, a Crusader, who, according to domesday-book, was lord of the manor in the 11th century, and is not unlikely to have been the founder of the Church”. This proposition is hugely confused and unlikely to say the least as Alwin Horne was lord of the manor before the Norman Conquest and is reputed to have died at Hastings in October 1066 so could neither have been the founder of the church nor a Crusader. The Victoria County History published in 1924 is more circumspect and describes the eastern one as being simply of a cross-legged knight in full armour, with his feet against a lion (Fletcher says a dog). Ashmole describes him as having a "loose Coate girt close to him" on which are the arms of Englefield. He is said to be in the act of drawing his sword, the lower part, which seems to have rested on a small dragon, but is broken away. Actually, from the position of his right hand he seems more likely to be sheathing the sword, perhaps a metaphor for death. It is supposed from marks on the effigy that there was formerly a shield attached and Ashmole notes "his shield is tore away".
He has the left leg crossed over the right, sometimes taken to mean the person portrayed took part in the crusades, though that theory is now largely disregarded. There is no record of who this represents, but the date appears to be late in the 13th or early in the 14th century, so we may therefore assume that he was the chief representative of the Englefield family at that period, none of whom is known to have participated in the Crusades. The only known soldier of around this period was John Englefield who went to Spain with John of Gaunt in 1386 and in 1393 expressed a wish to be buried in the Chapel of St Mary at Englefield, though this is much too late for an attribution of late 13th or early 14th century. The Englefield of that time was Sir Roger Englefield, one of the knights of the shire in the parliaments of 1307 and 1312, who died about 1317 and who this is now thought to be. This date is much too late for him to have been the builder of the aisle or, if the presence of the squint and bracket indicates what we think it does, the founder of a Chantry housed in it. Perhaps his presence here indicates a later endowment for the same purpose. This effigy is composed of a hard free-stone, which was the material generally used at that time, and was probably coloured though no traces remain.
The effigy under the second arch is a of a lady and carved from oak. She is also lying on her back, with her head resting on a pillow and has a curious head-dress fitting close to the head, and the wimple, the sign of widowhood, under the chin. There was colouring on this effigy too, though not now discernible. This effigy too is considered to represent a lady of the Englefield family dating from about the year 1340, now thought to be Joan Englefield, widow of Sir Roger, who died in that year. The presence of these figures of appropriate date may suggests that Sir Roger may have been the founder of the original chantry, of which the aisle formed the chantry chapel of St Mary.
Pevsner comments in The Buildings of England: “…it is altogether uncertain whether the south aisle went as far west as is supposed” and looking more closely it does indeed appear probable that it extended no further than the door and the original 3-arch arcade is then symmetrical. The west door, now hidden on the inside by the structure supporting the organ pipes since their removal from the Englefield Chapel dates from the 13th century though, meaning that the building always extended as far as it does now, but the door is both narrow and low and could certainly never have been intended as a normal entrance. A possibility is that there was a wall across just to the west of the main door and that the enclosed portion formed the original vestry, which was incorporated into the aisle during the Victorian restoration when the fourth arch was constructed and the new vestry built under the tower.
At the east end of the aisle are set in the floor four black marble grave stones. Three of these were described by Ashmole and are for Honora de Burgh, wife of John Paulet and daughter of Frances Walsingham, who died in 1661, John Paulet, son of John Paulet and Honora de Burgh, died 1660 and Honora Paulet, youngest daughter of John and Honora, who also died in 1660. John Paulet himself was still living at the time of Ashmole's visit but his gravestone was added in 1675. Fletcher also reports that in 1841 there were "some eulogistic lines" to John Paulet on the wall near the slab, commencing with the first six lines of the inscription on the monument in the nave. The Lysons in 1813 also describe this monument as being in the south aisle, exactly where is unknown but it must have been moved to the nave by Scott during the rebuilding of the church some 40 years later.