body: The short: my company have been paid to develop a software system for a client. There are (sort of) similar systems on the market already, there is currently a lot of demand for it, I want to redistribute something similar if I am within my rights to do so.
  
  
  I am not employed by the client, nor has anything formal been agreed (in terms of ownership) - but I have developed a system for them according to their design and requirements. I have not sold them this product as an off-the-shelf option, it is entirely bespoke.
  
  
  There are some features of this system that are arguably too bespoke, and technical approaches I have taken due to their own constraints, so if I were to aim to package it up for redistribution/sale to other customers, it would most definitely be different enough to the original, in many ways.
  
  
  My questions (with regard to my rights to sell it elsewhere as a product):
  
  
  
  
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  Does 'different enough' matter? I am assuming it does, but I do not know the law as to whether the intellectual property is theirs until the product varies from what they paid for? Am I concerned with the right thing here? How different must my product be? Is this quantified anywhere in law?
  
  
  Should I be concerned at all since nothing was in writing? Or are legal implications already made as a result of them paying the invoices I send them?
  
  
  What else am I not considering here? I have no clue about the legals with regards to this, but I am sure it must be well covered. I've signed contracts in the past (with other clients, in totally different industries) stating that I may not work for a competitor etc. within 6 months after project completion, but nothing has been formalised here.
  
  
  **EDIT: Apologies, I should clarify - I am based in the UK, so UK law is what I'm concerned with.**
  
  
  
title: Redistribution of system similar to the one commissioned (privately) by a client