Dealing with HMRC errors

JodieR

I had a client come to me shortly before HMRC issued all those 'sorry but we got it wrong' letters, but it's sort-of the same problem.
I'll not bore you with the details, but basically he's being chased for approx £12k tax spanning the last 10 years mainly because his tax code's always been wrong and despite telling HMRC several times they've never corrected it. He's also never claimed relief for pension contributions which I think he was hoping would reduce the liability (which it does) but I've also since found out that he's had other jobs which despite having legitimate looking P60s & P45s for just don't appear on any of HMRC's calculations they've sent me, which increases the overall bill further.
I know that he should have done more sooner to stop the situation spiraling out of control, but HMRC seem to be just as bad as him!
Does anyone have any tips on negotiating with HMRC to minimise liabilities when they've made errors? I'm hoping that others have taken on clients who received those letters and have successfully reduced the amount they're demanding.
Jodie

Monsoon

See if this applies to any or part of it:
http://www.rossmartin.co.uk/index.php/employers/essential-know-how/453-paye-underpayments-caused-by-hmrc-delay-esc-a19

JodieR

cheers, that might help a bit, now I just need to find some form of evidence that he did contact HMRC about this in the past.