The P45 is only a tax document, so the implications of not receiving one are minimal. If you have a letter from the company setting out the position, then that is fine for the purpose of claiming Jobseekers during any period of lay off.
A company can place you on temporary lay-off (it is very common, especially in the current climate) if this is allowed in your contract, or if it is custom and practice within your industry. If neither of these apply, then the company cannot place you on lay off without your agreement, and must pay you until they terminate your contract, regardless of whether they have work for you to do. However, if you do not agree to lay off, then the company may have to make you redundant. If you are made redundant in these circumstances you are entitled to minimum notice as per your contract and the statutory minimum notice requirements.
If you are placed on temporary lay off for 4 consecutive weeks, or any 4 weeks in a 6 week period, you can claim voluntary redundancy unless your employer can guarantee you 13 weeks unbroken work. In these circumstances you are NOT entitled to any notice period.
If there is no provision for temporary lay off in your contract, or in your industry generally, then you may well be losing your right to notice (or payment in lieu of notice) if you agree to temporary lay off. Of course, this has to be balanced against the possibility that if things improve you might still be able to keep your job.
For more information see here
http://www.citizensinformation.ie/e...ay_off_short_time_working_and_redundancy.html
The Irish National Organisation of the Unemployed also have an information line that deals with this kind of query 01 856 0088
If you are a member of a trade union, then they can also advise, and perhaps represent you in any negotiations with managment on the issue.