On Monday, 14 March 2016 15:52:47 UTC, Asha Santon wrote:
Disclaimer: This is a serious question which has everything to do with
how to count and nothing to do with religious beliefs. I ask it here
because some wise heads are present.

The date 1AD refers to the year a man I will call Yesus was born. It is
irrelevant whether it actually happened or not. Most of the world did
not know about it at the time anyway.

News of the event did not reach the British Isles for a very long time
so my question is this:

In the British Isles during the year we now call 1AD, what was the date
(year only)?

I don't even know how to look it up.
I am aware of the Gregorian, Julian, and AUC calendars but I don't want
to know what the date was in Rome.

Since we know the date he died, to the hour we can work ou that the year he was born was something in the region of October 3 BC or maybe 2 BC there wasn't year zero and all dates were given in respect of agencies other than the birth of a person in dispute.

The Roman year was decided arbitraily by the person in charge of the senate two chosen for each year -who had to show a profit or a victory by the end of the year which in one case was over 400 days long.

Dates were given as a comparison with rulers, usually cross referenced between rulers or sub-rulers. (E.g. "In the year of so and so when so and so else was so and so-ing and etcetera was etcetera.")

In Noah's time years appears to have been divided equally by constellations.. Julius Caesar had the court astronomers reckon the length of the year quite accurately and the year was divided into 10 months. Later this was changed to honour dead people (not called Februs evidently.)

The answer to your question would be there was no Britain per se as the Romans sub-let their colonies to regional kings. An annus would be reckoned from the ascendancy to each region's throne. The first year of the reign would be called the ascendancy (I'm not sure of the correct term.)

Thus the year would be spoken of as the nth year of the reign of so and so when tributary so and so became king and vassal so and so was regent of wherever and that sort of thing; naming plenty of people gave historians a chance to keep up to date by the time the newspaperslabs came back from the stonemasons.

The idea of dating years from the birth of Christ began with Constantine I believe but the marking of time still ran from the deaths of kings for most of the world. Whoever came up with the idea was motivated by ideology but it was most likely a convention worked out backwards and badly.

By the time of Mohammed the world was converting to papyrus. (The date of the invention of wood-pulp newsprint being lost to history.) No doubt keeping pace with page numbering systems that evidently confused not a few monks whose reliance on calf skins depended on the number of Egyptian manuscripts they could over-write.

You can see the point though?
History is subject to approval.