Late last night I checked my apache log remotely and access_log was only showing logs from early morning on the 4th of May, whereas previously it had been showing logs going back to the 26 or28th. I checked my security log and saw my ssh version had been scanned, I took heed of the "don't panic" message, and didn't:

Instead I decided to power off the box until I could be in front of it. When I got back I saw that all of my logs had started again from early (0400) 4th.
I don't know what's happened.
Have the logs simply started again for the new week? I would think this first only why not file off days and allow a backlog of 6 days instead of cleaning out the logs and starting again? If not this, what else could it be?

This was in my system log:
May 4 04:02:03 localhost syslogd 1.4.1: restart.

And this was in my Apache error log:
[Sun May 04 04:02:04 2003] [notice] Digest: generating secret for digest authentication ...
[Sun May 04 04:02:04 2003] [notice] Digest: done
[Sun May 04 04:02:05 2003] [notice] Apache/2.0.40 (Red Hat Linux) configured -- resuming normal operations

I really would like to know what's happened here, if anything?

Looks like logrotation! Did you configure weekly log rotation ? Check /etc/logrotate.d

Yeah thanks mate, I figured it out eventually. A cron process. I thought I would have had to setup such a process but apparently not! Also I was looking for a windows style archive file such as access_log-may2003 but instead were access_log.2 (which was there already, only now, it has data in it!)
Thanks again

Well you can always use piped log files with Apache v2 this works very well.