Have your rec'd a 'verbal' warning before this written one?
The manner, or way they choose to deliver the written one, holds no bearing in law. Employer can always state that they used the most 'cost effective way' - i.e., saving on postage - plus, that they were 100% sure you got it. Furthermore, it would be hard to prove that the person who put it thro your letter-box, knew, exactly what the contents of said letter was. They could state - say - if in a witness box - in their belief it was a letter stating that You would be well soon! Cold hard facts of life! As you have already stated, IT WAS a letter in an envelope, so to all intend and purpose, the persone delivering it, was unaware of it's contents. Different if it was a singing telegram & they broadcasted it to your street. I'm not making lite of your situation neilp, but that is how a panel / jury, would precive it. I've being Trade Union for over 35yr & know all the tricks of the trade! Honestly? Your best policy is to 'roll' with the punches on this one and try and improve the time keeping! If you have an illness, i.e., are a dibetic, then you may have some ground to work on and negociate timings etc. If not, the Employer can say that they were 'tolerant'. & that You had abused their 'Good Will'. Sorry, but I am just teling you the cold hard facts as ARE, But, to me, it seems in this case, No, the employer has not broken anything - in the eyse of the Law that is! Wish Icould tell you different!