There is a well-known and very marked reduction in the quantity of pottery discovered at sites in England after about the 1st quarter of the 5th century CE. This continues to be the case until about the 9th century.

My area is ancient rather than early medieval and I cannot go very deeply into specifics, but I can give a general outline of the question. We know quite a bit about pottery and ceramic production technology and techniques in the centuries before and during Roman occupation of England, ca 4th century BCE to 5th century CE. We can trace the expansion of the ceramics industry in England during this time, and especially its marked expansion under Roman rule. There is good evidence for the spread of technology, especially kiln design and updraft kilns in particular, and this happens in scattered areas even before the Romans arrived in earnest in Britain in the middle of the 1st century CE. From there, archaeology demonstrates a very clear expansion of production, with production centers at several places in the south, like the Severn Valley, Oxfordshire, Essex, and in the north, typically associated with legion garrisons, like Yorkshire or Doncaster. All of these sites will essentially be abandoned by the end of the 5th century BCE, and we find no evidence of updraft kilns or mass production of ceramics again until the late Saxon period, and then at new places like Lincolnshire.

This situation is perfectly in keeping with trends elsewhere in Europe at the end of antiquity, and is just one part of a larger economic disruption. Industries everywhere contract and become hyper-local in this period (we don't call it the "Dark Ages" anymore), sites are abandoned, populations shrink, Roman infrastructure breaks down and cannot be repaired (aqueducts, baths, harbor works, roads, industrial agriculture, etc). It is not that pottery ceased to be made in this period, but rather that pottery production returned to a very local activity, with very little movement of goods, and from what we can tell from excavations, there was a certain shift in (or loss of) technology such as the updraft kiln. The pottery that we do find is of a more poor quality, and there is much less of it. One can see an almost identical situation with ceramic production in Greece in the transitional period after the Bronze Age collapse.

It is also important to keep in mind that ceramic production was not limited to household items. Ceramic tiles were a major element in construction, and they were produced on a massive scale. With the end of Roman rule came an end for the demand for and knowledge of Roman-style building techniques: we see no more basilicas, no more Roman temples, no more Roman atrium-style houses or Roman villas. The demand for ceramic tiles disappears, so it makes sense that the centers which mass-produced them would become abandoned. Also important are large transport vessels like amphorae, though Britain was not a big exporter anyway. With the breakdown of trading integration between Britain and the rest of the former Roman empire, transport vessels became fairly useless. Most people and goods in Britain in the 6th century CE never venture beyond the boundaries of their hyper-local area, county or even village level.