He was unemployed for 4 months at the end of 2010 and claimed contributions based JSA - nothing else, as I was working p-t and just above the threshold.
Thankfully he found new work relatively quickly and he has a letter from the Job Centre thanking him for advising them of his change of circumstances and confirming JSA payments would stop the day before is new job was due to start. No more payments were made.
He has now had a letter from IR advising his that his tax code will be amended, meaning that he pays an extra £100 per month tax in 2013/14 due to them "previously advising you that you underpaid tax in a previous tax year"
That's it no, calculations, doesn't say which year and we have definitely not had any previous letter.
So, he's called IR to be told it relates to the tax year 2010/11 when he was paid JSA for 12 months, when he was working for 8. 
I'm really cross;
-It sounds like it's going to be a proper headache to get it sorted out (the JC letter is apparently not sufficient evidence to prove the benefit wasn't paid
)
-He was really reluctant to claim the JSA in the first place and now wishes he didn't
-How dare they send a letter implying he had ignored previous correspondence that wasn't sent (they haven't been able to supply copies)
-If they really believe he claimed benefit he wasn't entitled to, isn't there a bigger issue than just clawing it back. I thought benefit cheats were dealt with firmly (obv glad on this occasion that they haven't, but still...)