The information contained in this article is scattered around the website so this acts as a consolidating exercise to make the information contained within easier to find.
This article looks at slip of the pen errors on notices and some brief case-law. Most of the information is taken from Mannai Investment Co Ltd v. Eagle Star Assurance  UKHL 19.
Starting point – if it’s wrong, it’s wrong
It is worth starting with the important principle that if a notice contains an incorrect date, it will generally be ineffective.
In Hankey v. Clavering  2 K.B. 326, the lease was for a term of 21 years from 25 December 1934 with a break clause allowing either party to determine the lease at the expiration of the first seven years, by six calendar months’ notice. The landlord gave the tenant notice which said:
… I will be obliged if you would accept the six months’ notice to terminate your client’s lease which I am allowed to give on June 21, 1941. This would mean that he would have to give up the cottage on December 21, 1941.
This was clearly a clerical error and the notice should have expired on 25 December, not the 21st. Further, this will have been obvious to the tenant what the correct date should have been. Nevertheless, Lord Green M.R. said –
“This appeal raises a short point in connection with a break clause in a lease wherein the plaintiff was the lessor and the defendant was the lessee. By his letter of January 15, 1940, the plaintiff, on the face of it, was purporting to determine the lease by notice on December 21, 1941. The whole thing was obviously a slip on his part, and there is a natural temptation to put a strained construction on language in aid of people who have been unfortunate enough to make slips. That, however, is a temptation which must be resisted, because documents are not to be strained and principles of construction are not to be outraged in order to do what may appear to be fair in an individual case.”
His reasoning was as follows –
“Notices of this kind are documents of a technical nature, technical because they are not consensual documents, but, if they are in proper form, they have of their own force without any assent by the recipient the effect of bringing the demise to an end. They must on their face and on a fair and reasonable construction do what the lease provides that they are to do. It is perfectly true that in construing such a document, as in construing all documents, the court in a case of ambiguity will lean in favour of reading the document in such a way as to give it validity, but I dissent entirely from the proposition that, where a document is clear and specific, but inaccurate on some matter, such as that of date, it is possible to ignore the inaccuracy and substitute the correct date or other particular because it appears that the error was inserted by a slip. By the clear wording of this notice the plaintiff purported to bring the lease to an end on December 21, 1941. In so doing he was attempting to do something which he had no power to do, and, however much the recipient might guess, or however certain he might be, that it was a mere slip, that would not cure the defect because the document was never capable on its face of producing the necessary legal consequence.”
Although this applied to a contractual break clause, the principle applies to all notices and that is why most section 21 notices containing the wrong date are held to be invalid even in a situation where it might be obvious to the tenant what the correct date should have been. (Now perhaps less of a problem since Spencer v Taylor).
Exceptions to the general rule
There are however exceptions to this general rule where there is a latent ambiguity in the notice.
For example in Doe d. Cox v. Roe (1803) 4 Esp. 185, the landlord of a public house in Limehouse gave notice to quit “the premises which you hold of me … commonly called or known by the name of The Waterman’s Arms.” On the evidence, the only property let by the landlord to the tenant was a public house called The Bricklayer’s Arms; moreover there was no public house in Limehouse called The Waterman’s Arms. The notice was held effective in respect of the tenancy of The Bricklayer’s Arms, the case being treated as one of latent ambiguity.
Another example occurs when a date is specified in the notice which, as is plain from the face of the notice, was obviously stated in error for the true date which the giver of the notice must have intended to specify. This will usually occur nowadays through a simple typing error. In such a case, the date so given can properly be construed as a reference to the true date.
If the error is contained in a tenancy agreement (such as the wrong rent), rectification may need to be considered for which see this article.