Not so illegal, in reality, it seems.
http://www.hmrc.gov.uk/working/forms/paye-forms.htm#4
If you've lost your P60 your employer can issue you with a duplicate. Since 2010-11 your employer no longer needs to show on the P60 that it is a 'duplicate'.
@Sparky started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
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Not so illegal, in reality, it seems.
http://www.hmrc.gov.uk/working/forms/paye-forms.htm#4