What did intrigue me, however, was how on Earth the Powers That Be work out when Easter actually is in Britain. It seems to float around the calendar quite merrily. So here's the answer:
First you need to get the date of the Spring Equinox. That should be between 21st and 23rd March in any year, when day exactly equals night with 12 hours between the sun going down and coming up.
Next you need to know the date of the subsequent Full Moon. This year that will be on Tuesday 15 April.
Finally the next Sunday is Easter Sunday! So this year that's 20 April.
Now, if either the Spring Equinox coincides with a Full Moon or one falls on a Sunday it may require a little closer examination as to precisely which came first but hopefully that won't happen very often. My guess is that this all comes from interpretation of a sequence of events in the Bible. In which case, why do people in other versions of the same religion come up with different dates?
That I still haven't an answer for. But maybe someone out here has.