The House of Lords in Buchanan v Alba Diagnostics Limited  UKHL 5 has confirmed that it is implied that in a purchase or assignment of a patent, the right to improve it is given. The reason for this is to avoid the situation where the vendor, after selling the patent, comes up with something that, without being an infringement nor an improvement accomplishes the desired object in some other way and therefore destroying the value of what has been purchased. Â
In Buchanan, the meaning of improvement was settled by saying that it is not a term of art and canÂ have wider or narrower meanings according to the context. In the present case the court held thatÂ a part for a machine, although it may be strictly considered another product, is an improvement asÂ long as it can be fixed to the machine and it adds efficiency or value to the machine to which itÂ is attached.
In Buchanan, the court has tried to give an answer to the question: ÂIs, in a patent agreement, a clause reserving the right to improve the patent a void restraint of trade?Â This was answered in the negative, following Esso Petroleum Co Ltd v HarperÂs Garage (Stourport) Ltd  AC 269, 300. However, it must be noted that the decision in Esso is reached after balancing the bargaining powers of the parties and the traderÂs interest (in a similar way as if it was the case of anÂ unfair contract clause).