At first blush, you might assume that whoever pays for something would then automatically own the intellectual property rights in the resulting work products…but unfortunately you would be wrong.
Under English law, the basic principle is that the first owner of new intellectual property rights will be the “author” of the materials in question.
So, if you pay a developer to create a new app for you, they will be the author and will own the IPR in it, and all you will have (in the absence of an express contract to the contrary!) is a more limited licence to continue to utilise the materials for the purposes for which they were commissioned.
So, whilst you may still be able to use the materials yourself and potentially even use them to licence to third parties etc, you equally could NOT prevent their use by the developer with other people, even if that resulted in a loss of commercial/competitive advantage.
So far, so worrying.
However, the good news is that the IP ownership issue can be regulated by contract provisions (assuming that you have a proper contract in place!).
So, if you are paying someone to develop an app or product which you intend to market to third parties (and in respect of which you will accordingly want to both confirm your own usage rights and stop third parties from using it without your permission), you will want to make sure that your contract assigns all new IPR to your exclusive ownership.
You may also want to contractually preclude the developer from providing the same or similar services to any of your competitors, at least for a short “lock in” period of time which will enable you to establish the market for your product or offering.