P45 should be given to you (and sent by employer to the Revenue) immediately upon termination of employment.
A P45 however is not strictly evidence of termination of employment, and also just because you don't get your P45 doesn't mean that you're still employed.
You should have received notice that your employment has been terminated (not necessarily in writing), although again that is not always given either, but it is your statutory right once you have been working somewhere for at least 13 weeks.
I was told the yesterday that the boss has no work for me, as I could not get onto a site, my card was out of date. Social welfare said I need to get a P45.
Social welfare generally require a P45 for a Jobseekers claim, but if you don't have one, then get a letter from your employer to confirm position, this will do.
Make sure your claim is in, even if it doesn't have the supporting documents, and you will get backdated (although first three days of a Jobseekers claim are not paid in any event!).