Seems a bit unfortunate, but unless she had a new contract that outlined her new duties, which was signed & dated by herself & employer to signify the change of role & pay 2 years ago, then I doubt that anything can be done. However had there been a clear verbal acknowledgement of additional duties and extra pay (at the time of the occurance) then this might stand (although perhaps in this case there wasn't, hence it doesn't seem clear as to when the entitlement would occur).

A quote from the CAB website regarding overpayments:

"However, if there has been a genuine overpayment of your wages, your employer doesn't need your consent to recover this. They can make a deduction from your wages without your agreement. There are some exceptions to this rule and there are special rules about deductions made from shop-worker's pay."

Another thing is that the UK minimum wage for someone =>21 yrs went up to £6.50 / hr from 01 Oct 14, so she's not actually getting a payrise for taking on new duties, albeit if she was being paid £6.20 prior to the age of 21 then she was on more than the minimum for 18-20 yr olds in that period. Hence if she is now taking on new duties then perhaps she should be getting more than the minimum wage.

Minimum Wage Bandings shown as: >=21 / 18 to 20 / Under 18 / Apprentice*

2014 £6.50 / £5.13 / £3.79 / £2.73 (as of 01 Oct 14)
2013 £6.31 / £5.03 / £3.72 / £2.68
2012 £6.19 / £4.98 / £3.68 / £2.65
2011 £6.08 / £4.98 / £3.68 / £2.60
2010 £5.93 / £4.92 / £3.64 / £2.50

Of course, this is all just general advice from a keyboard legal "expert" - she should either put it down to experience and carry on (if she's happy working there still) or seek legal advice / CAB (which might cause futher "issues" with her continued employment).

Perhaps the company could take the money over the same timescale that it underpaid her?

To be honest, I said similar to her - I couldn't see how a company would just hand over £2000 without some sort of communication by letter, but she seems adamant that it all went through on the say so of her supervisor.

It seems to me that somebody in payroll as probably had an ar$e kicking and now they are trying to recover their cash.

It seems, from my albeit very limited knowledge on these matters, a tricky one and, I would imagine, a relatively rare case.

As it's not a case of the employee being slightly over paid each month over a long period it's not a case where the employee "should have noticed". It's more like a case where the employee is given a bonus and then the company change their mind. It's not a clerical/transaction error either.
As she'd been promised it by a more senior member of staff and then received it she'd have been well within her rights (in my very inexpert opinion) to have spent it already. She could've gone out and booked a holiday or bought a car.

I can't see how, in any fashion, the company can just not pay her next month. I think the worst that'd happen is she'd have to repay it in instalments over a long period as Sal suggests. Though personally I don't see why she should repay it at all. The company made a decision to pay her, just because they don't like that decision now is just hard cheese.

But sadly my opinion on things isn't always the reality, otherwise Nigel Farage would be deported to Eastern Europe.

Like any 21 year old, im sure she has already blown the bonus she received? if not, I would pay it back so then she can receive a wage for 2 months. Its easy to see whats happened here, the difference in wage of 30p is the difference between what she was receiving and what a 21 year should receive under the minimum wage so the payroll department have messed up and back dated it more than was necessary. The company is quite within their rights to ask for the money back, whether not paying someone for 2 months is the way to go, I dont know. If she doesnt like working there, she could quit, citing constructive dismissal as she was under the impression this bonus was legitimate so spent it and now she has to work for 2 months unpaid which is not an option.

Regards

King James