Copyright on code from public source
<p>Let's imagine consultancy A develops a code for client B that use some free available code from a website so it's a derivative work from the free code (MIT license). Can consultancy A re-use the same derivative work in for client C without copyright infringement due to client B? </p>

<p>The consultancy can definitely work on the basis of the MIT-licensed code.  However, if the contract between A and B specifies that B gets the copyrights for the developed software and A does not retain rights, then the modifications that A made for B may not be used for C.  If A retains copyright, then there's no problem.</p>

copyright united-kingdom intellectual-property software open-source-software