Hi there, the information contained in the letter would have been personal data protected under the Data Protection Act. Even if it is in the public domain it does not mean it is not protected and the last couple of paragraphs of the first page on the Data Protection policy summarise this quite well.
So whilst there is a potential breach here, there are also mitigating factors which you can use in your defence. First of all, this was done following a request by the customer that you do so. Therefore you can say that they have specifically waived their right to privacy in the circumstances by asking you to leave the invoice on the desk.
There were also no losses suffered by the customer or business and the only person who took the invoice and saw the information inside it as the customer, to who this data relates. So it is not like you left it there and an unrelated third party took it – the intended recipient took it and their privacy was not breached.
So all in all, this could be a misconduct offence but not one which should be considered serious enough to justify dismissal. The employer should perhaps issue a warning to warn you about your actions and ensure you do not breach these rules again and only repeat offending should result in dismissal.
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