Tax Code 0T

For some reason my tax code on my last p45 (from job centre) is 0T - from what I can deduce on the internet this isn't the correct code for me and is usually used when people fill in a p46 - and then it gets sorted out a month later.

Does the same principal apply when it's on the p45 - ie will I get overtaxed this month, then it'll get worked out correctly next month? Or am I better off filling in the p46 now to save hassle further down the road?


Thanks

Edit: Thinking about it I'm not sure I've even posted on the right board. I'm so hopeless!