i received two letters from the tax office today both stating i had underpaid tax £758 in 2008-9 and £1348 in 2009-10. turns out the second is the total amount not a separate amount as i first thought. i immediately phoned them and said there must be a mistake as my employers wouldnt have made that kind of mistake. how wrong i was. my civilian employer had paid the correct tax and the correct rate but my TA pay was the one at fault. as a secondary income it comes under the Base Rate of tax. for some reason they had it as 645L which means no tax was paid. i earned less than 4k with the TA. i now owe a lot of tax through no fault of my own. i checked the tax code and as it was the same on both so i assumed incorrectly that i was paying the correct amount. apparently it is my responsibility to ensure i am on the right tax code but how the hell am i supposed to know? i do not earn a lot of money. i only work part time due to cutbacks and only earn around 16k a year. £1348 is more than a months wage for me at the moment. i cannot afford the loss of that sort of money. i asked why they didnt inform me when the amount owing was only £700 but was told it had only just come to light. i dont claim any benefits and am only just keeping my head above water even before this bombshell arrived. what can i do?