Unpaid work in multi national retailer

I think it really depends on the situation. Say you work in a small place and you do an extra bit on top of your stated hours, well I wouldn't really have an issue with that. As long as it's not taking the piss.

In some jobs people put in horrendous hours, but there is an expected payoff down the line for doing so. A solicitor being made partner, for example.

Some time back I read an article about this in a German paper and the tax authorities there actually regard this as fraud, since the worker not being paid means that the taxman does not get his cut of the income tax that would have been due. Not sure if or how they actually pursue such cases, but no doubt it would involve disgruntled ex-employees. Not sure how Revenue here looks at it.