Hi I'm hoping someone out there with a bit of tax knowledge can help me, very stressed here 
DH worked at the same place (Company A) for a few years, last year it was bought out by a large company (B) and he was TUPE transferred across.
About six months later, he noticed that a new (lower) amount was going into his bank account every month, on querying this it seems that the Company B is now paying the correct amount, but for the first few months had not been deducting enough PAYE.
Company B never sent out any paper payslips but uses an online system which DH unfortunately hadn't been keeping as close an eye on as he could. The transfer/extra pay also coincided with other significant (unrelated) changes to our finances so the upshot is we didn't notice any extra money coming in. Company B say the mistake occurred because A didnt send DH's P45 over with the rest, apparently they did ask for it but didn't get it, didn't chase it up, and didn't ask DH for any details (but clearly knew his salary!)
We've been stressing and stressing about how and when we're going to repay tax but I've just spoken to a friend who says she had a similar issue and that the employer had to repay the tax, not her, as it was their error. Anyone know if this is right?!