I remember reading in James Campbell's essay "Was it infancy in England", that traditionally historians, implicitly or explicitly, assumed that there weren't any Jews in pre-1066 England on the presumption that late Anglo-Saxon England was too economically backward to have any need for Jewish credit. Since the 1970s that position has become increasingly untenable - 10th and early 11th century England seems to have been above the Western European average in terms of urbanisation and to have had an already very monetised economy and thriving trade with Flanders and Ottonian Germany - and so as Campbell suggests, there must have been some kind of royal decree preventing Jews from coming in that William the Conqueror and his successors revoked that simply hasn't survived to us. Still, there's no way of proving that so what are the other possible explanations for the apparent absence of Jews in pre-Norman England. Then there's also the question of whether there were any Jews in Roman Britain, given that there were quite a few Jewish communities in Gaul and trends in recent scholarship have also argued that Roman Britain, especially in the 4th century AD, was a lot more cosmopolitan and a lot less of an underdeveloped imperial periphery than historians have traditionally assumed. If there were, then why did they apparently disappear after the Roman legions left.
Even in current standard overview works like Chazan 2006 and Abulafia 2011, it was not at least until the last decades of the tenth century that we can confirm some traces of the activity of the Jews in North-Western Europe, i.e. north to the Alps. In short, Anglo-Saxon England had been not an exception, but also it belongs to the broader pattern as northern France and Flanders did. Only the region that Anglo-Saxon England had had a strong cultural and trade connection with pre-1066 and in which we could find the possible settlements of the Jews was the Rhineland, such as Cologne, though probably not the all towns in the region had a Jew population there even in 1066.
It is true that the Jews, especially north to Alps, tended to have almost been very difficult to detect from the 5th centuries to the early 10th centuries. Their settlement seemed only to have survived in southern France (up to Lyon).
The following is an excerpt of the oldest confirmed dates of the Jewish settlement in high medieval German towns. You might be surprised the lateness of some dates, though they are terminus ante quem:
The earliest datable written evidence of Jewish settlement (or at least of plans for such a move) comes from places on the eastern periphery of the Empire: palaces in the poorly developed cities of Magdeburg on the Elbe (965) and Merseburg on the Saale (982). For the pre-Crusade Jewish settlements in Regensburg (981), Mainz (1012), Worms (1034), Cologne (1010/12 or 1044), Prague (c. 1090), and Trier (1066, or at least long before 1096), we have only sporadic ante quem datings. (Haverkamp 2015: 12)
Then, why did the Jews came (or made visible) sometimes quite a later than the alleged rise of the economic activity in NW Europe?
The recent researches attempt to explain this mystery mainly from two points of view.
1. The Jews wished to establish themselves firmly in the town in a sense of somewhat legal community by the privileges of the local ruler.
Both Abulafia and Haverkamp emphasize that many of these towns with a new Jewish settlement quarter were either directly founded by the Ottonian ruler or cathedral cities in which the bishop governed both the bishopric centered the city as well as the cathedral city itself (Abulafia 2011: 39 and passim; Haverkamp 2015: 12). They even suggest that the ruler of the city like the emperor or the (arch-)bishop invited into the city and contracted with the privilege to promote their commercial activity. Haverkamp especially regard the relationship between the Christian bishop and the Jewish community as the latter's patron as very important in Ottonian and Salian Germany (i.e. the late 10th to the first half of the 12th centuries).
The most famous example of such a privilege was formulated in the charter issued by Emperor Henry IV of HRE to the Jews in Speyer and Worms (c. 1090). He guaranteed:
In other words, the majority of the Jews did probably not simply went diverse markets across Europe and settled in such cities just as they like. Compared with these cases in Germany, I suppose pre-conquest Anglo-Saxon England (at least until the end of the 1st millennium) did not have enough counterparts of these middle to large size city with the local ruler who could patronize the activity of the Jews as they could in contemporary Germany.
2: Some moral troubles of the Jews on the trade within the non-Jews
Citing a Jewish scholar's work (Soloveitchik), Abulafia also argues that the change of the interpretation of Jewish law (halachah) around the year 1000 enabled the Jews to trade more extensively with the non-Jews, with help of money-lending as a loophole of the direct trade of money/ goods (Abulafia 2011: 40). To give an example, she points out that the Jews had in principle been forbidden by their own religious law (not by the Christian one!) to trade wine directly with the local non-Jewish population, but now they could receive such a good for trade 'as a repayment for the credit'. In other words, the Jews in High Medieval Europe certainly had less remorse of conscience to trade extensively with diverse people than their early medieval ancestors, so they must found quite a large room for newly permitted commercial activities also in North-Western Europe first around the 11th century, not so much earlier.
References:
(Edited): fixes typos (sorry).