UK employment law: Are hours recorded by a clocking in system legally binding?

[pjvenner]

Last week my pay pay packet was missing a day's pay, on questioning this I was informed that it was because I failed to clock in on that day. The clock uses punched cards, not the old type that stamp the time on the card so I can't say whether I forgot to clock in or whether my card was misread [this has happened before & I brought it to the attention of a supervisor who just said I must have swiped it too quickly]. After verifying with my supervisor that I was present they rectified my pay but warned me that if it happens again I will lose pay.

I am on minimum wage already so any missing pay will mean that I get paid less than the national minimum wage which surely must be illegal unless the employer can prove that I didn't work that day? I work in a crowded environment so I doubt there'd be much of a problem finding witnesses to verify my attendance, even though some may feel intimidated about speaking up against the employer.

Any references to legislation or previous case law examples would be greatly appreciated.

Note: I'm not in any union and as far as I'm aware there is no union presence at all in this company. I've worked there just over a month so I know I have very limited rights but I don't think the right to receive the national minimum wage hourly rate is limited in any way.