What is "underpayment restriction"?

[leboof]

Hi and thanks for taking the time to read my post and hopefully help!

Can some one explain "underpayment restriction" please. I'm cofused about the word "restriction" and even more confused with HMRC's explanation.

Is it simply underpayment of tax?

This is why I ask:
I earned some money from another source other than my main employer. Having declared the earnings, last year the HMRC changed my tax code to collect the tax owed on this amount. Fine.
This year I received an even lower tax code stating I may remember I owed them money....

BUT surely they altered my tax code to collect the money last year, so why are this saying I still owed them money?


"underpayment restriction -£1900"

Thank you in advance for your replies.

[Mikeyorks]

Yes the £1900 restriction is to collect an earlier year underpayment of (£1900 @ 20% =) £380.

Can't explain the earlier coding out as it partially depends when in the year it was done and if it was a Month 1 code in order to restrict the amount collected each month. A bit of a clue might be how much the £380 relates to the original underpayment?