Tax code error and underpayment

[dpw999]

I have been hit with a tax underpayment for 2012-2013, and have been trying to work out why this occurred and whether I am likely to be able to claim employer or hmrc error.

My personal allowance was initially applied to a zero hour contract which was my main job. I subsequently received a second employment contract for a full time post with the same employer whilst keeping the 0-hour contract for locum work, and therefore completed a p46. It seems however that my zero hour contract remained as my main job for tax purposes even though they were aware of change in main job. Within the same year I also moved job again to another employer and completed another p46 .
Stating again that I had a second job. Once again I was kept on BR code and as I strayed above the higher rate threshold didn't pay enough tax. I assume.

Holding two employments with the same employer , am I wrong to expect them to apply the correct tax code to the relevant job? And I believed that by submitting a p46 this also informed the hmrc of change on circumstances and prompt a review of my tax code?

[RMC]

Why do you think your employers used incorrect tax codes? This usually happens when the prospective employee gives incorrect information (=ticks incorrect box) on P46. Did you do that?
Please don't forget: if in 2012/13 you received other income such as taxable interest or dividends, you must tell HMRC and pay higher rate tax on that (and, possibly, add-ons). Ignorance is no excuse for late filing.