Hi.If you didn't file your 2012 tax return by 30 December 2012 then you cannot have any underpayment coded out through your tax code for 2013/14. The tax office will not give way on that. If they start breaking their own rules, then there will be a queue of taxpayers demanding the same treatment. I've been working in tax for over 30 years and I've not seen one taxpayer succeed in having an underpayment coded where the deadline for submission of the tax return has been missed.The problem you have is that if you don't pay the tax soon its collection will be outsourced to a commercial debt collector who won't stop pestering you until it is paid. What I suggest you do is make direct payments though internet banking or by cheque of £75 to £100 month. If it was collected through your tax code over one tax year, you would be paying £75 per month in additional tax to clear it. The tax office will not relent and the longer you leave it without making any payment the more likely that the commercial debt collector will get involved. If the tax office can see that you are making an effort, they may leave you alone. There are far bigger tax underpayments that the tax office need to collect but they won't wait indefinitely so you should start making payments as soon as you can. You could try calling the Business Payment Support Service on 0845(NNN) NNN-NNNNto arrange a payment plan but they usually only deal with tax payments where the payment deadline has not passed. You might also try calling the Collector of Taxes to agree a formal payment plan on the number on any tax statement that you have or on the number here. If you can agree a plan, then you won't be contacted any further unless you miss a payment. Take a look here for information on the different methods of paying tax.I hope this helps but let me know if you have any further questions.