Mwalusanya, J.: This is a suit over a contract of sale of a vehicle between Tanganyika Bus Service Co. I Ltd. (the plaintiff) and National Bus Services Ltd. - Kamata (the
A defendants). The defendants invited tenders for the purchase of its bus reg. no. Su. 17719 Fleet No. 140. The plaintiff was one of those who offered to purchase the said bus. The defendants vide its letter dated 1/7/1986 which is Exh.A in court accepted the offer and asked the plaintiff to pay cash shs.580,280/= and collect the bus before 24/7/1986. The plaintiff duly paid the Shs.580,280/=. However when the plaintiff's Traffic Manager Mr. R.S. Sandhu (PW.2) went to B collect the bus on 18/7/1986 the defendants refused delivery of the same. According to the defendant's witness Mr. Jovin A. Lyimo (DW.1) who is also the defendant's Corporation Secretary, they refused delivery because there was a C mistake in the award of the tender to the plaintiff. The witness testified that they wanted to award the tender to the highest bidder but by mistake the plaintiff was awarded who was not the highest bidder, and so it is said that the highest bidder one Yohannes s/o Sanga should have been awarded the tender. D
As a basic statement, mistake in contract does not affect the validity of the agreement. It is only when there is a mutual mistake, that mistake can affect the validity or enforceability of a contract - see the decision of the Privy Council in a case from Kenya Sheikh Brothers Ltd. v Arnold Julius Ochsner  E.A. 86. The Tanganyika Contract Act Cap.433 E in s.20(1) states:
Where both the parties to an agreement are under a mistake as to a matter of fact essential to an agreement, the agreement is void.
F The crucial phrase is 'both parties', because, the fact that only one party is mistaken will not affect the contract, unless one is led into his mistake by the actions of the other party. But in here it is common ground that the plaintiffs had nothing to do with the mistake allegedly made by the defendants. G
As for a unilateral mistake by one party to the contract, the law is that it will affect the validity of the contract only if the doctrine of Non est Factum (it is not my deed) is successfully proved. Non est factumis the name given to the argument raised when the defendant in a contract suit alleges that a document which he has signed should not be binding H upon him, because he was induced to sign it on the understanding that it was of a completely different nature from what it is in fact. That is a very difficult point to establish because the mistake must be one relating not to the content but to the I character of the subject matter. The document signed should
A be radically different in character from that which the plaintiff believed he was signing. As Lord Reid pointed out in the decision of the House of Lords in Saunders v Anglia Building Society:  3 All E.R. 961 at p.964 that
B There must I think be a radical difference between what he signed and what he thought he was signing - or one could use the words 'fundamental' or 'serious' or 'very substantial'. But what amounts to a radical difference will depend on all the circumstances.
C So the essence of the plea non est factum is that the person signing, believed that the document he signed had one character or one effect whereas in fact its character or effect was quite different. But that is far from the case in here because the difference is very narrow indeed i.e. between two bidders who were the highest bidders.
D In my view the mistake in here did not go to the substance of the whole consideration or to the root of the matter. The plea of non est factum is a plea which must necessarily be kept within narrow limits on the ground that no man should take advantage of his own wrong. Negligence or carelessness or inadvertence on the part of one raising non est factum E would therefore prevent the doctrine being effective and that signing a document without reading it or appreciating its consequences is prima facie negligence. I think the doctrine should only be available to those who are senile, blind or illiterate or in some other way quite incapable of comprehending the document presented to them for signature. For that F reason an order of specific performance will issue as prayed.
The plaintiff has also asked for shs.10,000/= being special damages. He said that those were the expenses incurred by the traffic manager (PW.2) and the driver and the turnboy when they made an abortive trip to DSM from Mwanza to G collect the bus. The expenses are for food and accommodation for some ten days or so. The General Manager of the plaintiff company Mr. S.B. Hassanali (PW.1) produced a receipt (Exh.B) being the cost of expenses that were paid out to those three employees. No challenge was offered by the defendants to those damages. And in my view those H damages are payable because they are direct, foreseeable and reasonable, and quite in line with the rule in Hadley v Baxendale: (1854) 9 Ex.341. I accordingly award the same to the plaintiffs as prayed the suit. I