Thanks Tony. I'm not that keen to get my employer involved as I don't want to cause any problems in my job. Would a P45 being issued by my first employer have indicated to the tax man that the role was not secondary employment and add weight to my argument? Did they put me on this BR tax code or was this the fault of my employer?
I also overpaid tax in the following tax year 2011-2012 as they switched me to a higher rate second job tax code for a while but I then did not go back and check previous tax years and this was refunded immediately. Had I known about this underpayment at the time I would have offset the 2 payments. Could I use this to indicate I thought my tax affairs were in order ...i.e. I did not notice either the overpayment or underpayment of tax. I get the feeling that the likelihood of this being cancelled is very low - is that your impression?
Thanks for your help.