What does the tax code 522L/1 mean?

New Tax code 670L M1. after claiming for laundry expenses. What does M1 mean?

• In August I called my tax office, to claim for my flat rate laundry expenses. I claimed for the previous 6 years. My tax code adjusted (eventually) from 603L to my new code 670L, after receiving in writing that my allowance is £140 per year. I have just received my pay with the correct tax code, but no rebate/less tax. So I have drawn the same pay even though my tax office said I would pay less tax. My pay slip states 670L and M1 after it, does anyone know what the M1 means?

• Answer:

  This means each month's pay is taken in isolation. Not normally done when code increases, but always where code decreases. The only times I have known month 1 issued with a code increase is if there is a known or suspected underpayment coming up, and HMRC doesn't want employer to give you a refund. Check it out with HMRC. Your code would normally change to 617L. It looks as though your refund for back years is being credited through your code number, although the month 1 stops this happening. You do not have to accept this, and can ask for a cheque.