Out of curiosity: "the worst" out of what? Centuries? Centuries in England? Centuries leading up to and including the 13th but not anything later?
That's a difficult statement to make or verify.
The 13th century was definitely the worst for the Jews OF ENGLAND. That's not just a reflection of the fact that for three centuries after this there were none- it was legitimately very bad, with riots and arrests against the Jews leading to thousands of deaths, a blood libel, Jews being forbidden from moneylending (a major source of their income in a place where they were barred from many other professions), Jews being forced to wear identifying badges, all Jews being arrested in 1278 for coin clipping... all of this before they were finally expelled.
And yet I would argue that the very next century was worse for Jews in other places. In the 14th century,
- Jews were expelled from France twice (1315 and 1394), the second time lasting for more than 200 years
- Jews throughout Germany and other parts of Europe were expelled and/or massacred in the wake of the Black Death, which Christians believed was caused by Jews poisoning the wells
- the 1391 riots in Spain led to the deaths of many Jews and the "compelled" conversions of thousands more, the beginning of the end of Spanish Jewry (the beginning of the process leading to the institution of the Inquisition in the 1480s and the Expulsion in 1492)