Architecturally a fascinating building with parts from every century between the 12th (Norman, above) and 19th (except possibly 17th), including a Georgian attempt at the Perpendicular.

The earliest parts are the beginning of the two W towers ... The towers were begun about the middle of the C12. They have broad buttresses shafted all over ... In addition the SW tower has intersected blank arcading on the lowest level. ... The Norman intersected arcading is followed by a small Transitional one, with waterleaf capitals and pointed trefoil arches, and then proper E.E. plate tracery appears, and above that the C13 bell-openings with bar tracery. In both cases the motif is an unfoiled circle. So the tower was complete by c.1260-70. Then, in the C14, a new bell-stage was added. There was a tall lead spire as well, but this fell in 1741. The other tower is externally Perp throughout, with much more bare wall. Only one small window below the clock, with two continuous chamfers, indicates an earlier date. The tower was built from 1453 onwards. ... A spectacular W window of seven lights between the towers, a statue in a niche above, and a doorway below which is thinly shafted  and stands in a shallow porch. ... Panelled battlements on the porch. Three-light aisle windows and three-light clerestory windows. Attached to the NW tower on the N side is a tall chapel with entrance from the E side. This is what remains of an outer N aisle. ... 

Perpendicular nave (first picture). ... The crossing tower (second picture) is short and featureless. In the Middle Ages it carried a lead-covered octagonal wooden lantern, modelled probably on that of Ely. ...The transept exteriors are again Perp, with much plain wall and big end windows of five lights. ... The chancel aisles have Perp windows. The S chapel is five bays long, the N chapel only three. The S chapel was building in 1433, when money was left for the job. The chancel E window is a remarkable rose under a pointed arch with quatrefoiled circles in the lower spandrels. It is largely reconstruction, after fragments had been discovered in 1872. ... Below the rose window, are three tall Perp niches. The clerestory of the chancel is Perp too, with three-light windows.  

(The tower) buttresses also show inside the church. ... The arch towards the nave shows in both towers; that towards the aisle is in its Norman state only in the SW tower (third picture). The arches have shafts with decorated scallop capitals. The line of the Norman aisle roof is still visible above the SE arch on its E side.

In addition, the SW tower has a very impressive wall passage on the first floor. This has stepped tripartite inner arcading familiar from the clerestories of Norman cathedrals and abbeys. The short columns are Norman, the tall ones E.E., ...

Nave. The Perp interior of St Margaret is, alas, disappointing. It is of 1745-6, an attempt by Matthew Brettingham .. to be Gothic, an attempt inadequately rectified by (Sir George Gilbert) Scott in 1875. Five bays, piers with four shafts and four hollows, 'basket arches'. ... The reason for the rebuilding was a storm which blew the spire of the church down. The king as well as Sir Robert Walpole gave £1000 for rebuilding. The nave originally had a flat stucco ceiling.

Chancel. The Norman church was completely rebuilt in the C13. Chancel, crossing, and transepts are internally in the state then given them. ... Today's length of the church  is that of the C13. ... The crossing has tall arches in all four directions, those to E and W being the more ornate ones. They have stiff-leaf capitals, simpler than those of the chancel, and finely moulded arches. ...
Reredos. By Bodley, 1899, with many figures and foliage.

The chancel has vigorous composite piers based on the motif of four attached shafts. In one pier there are thin diagonal shafts as well, in another these are keeled, in yet another there are slender hollows instead, and in the fourth the round core appears behind the sturdy shafts. All piers have beautiful, ample stiff-leaf capitals. The abaci vary without system between a form adapted to the piers and an octagonal form.
Screens. Behind the stalls and otherwise between chancel and aisles a number of C14 screens, that is of dates earlier than most surviving screens. ... all have ogee forms and crocketed gables. One has two-light divisions, the other three-light. The latter has reticulated tracery with small motifs in the reticulation units. ...

The clerestory of the chancel has a wall passage with detached arcading, and the remarkable thing is that this motif must be taken over from the E.E. clerestory; for the clerestory shafts have have E.E. leaf capitals and were only lengthened and provided with new Perp bases. 

In the crossing to the N a screen of 1584, but in its inscription also referring to King James. Dado with blank arches, above two tiers of open arcading. ... Organ case. Rococo. By Snetzler, 1754.

Along the south side of the church precinct, in Priory Lane, a range, 180 ft long, which is all that remains of the small Benedictine Priory of Norwich Cathedral established at Lynn about 1100. Of the remains the only externally prominent piece is a broad archway with four-centred head. (Inside, however there are several windows and arches which point to the C14 ...)