In my previous job I applied a small bit of Python code that I had previously developed during my academic studies. I made clear that the IP was mine and that, because I generated it in the past, the company did not have ownership over it (there was a clause in my contract that any IP generated during my employment, whether in work or non-work hours, belongs to the company. This is fairly standard in my industry). When I left the job I took the code with me.
My old company slept on this somewhat, and now want a version of this code. They are willing to pay me for the time to develop it into something usable for them, which I estimate would take a few days and that I could charge about £500-2k for, considering typical day rates in my industry.
Financially I would like to do this small piece of work, which could be done in evenings and over weekends. However, in my new job I have a clause that states that:
You shall not work for anyone else, whether paid or unpaid while you are employed by the Company or have any financial interest in any capacity in any other business, trade, profession, without prior discussion and written agreement from the Company
What is my best course of action here? Do I have a legal/moral obligation to tell and get permission from my new employer or is it something that I could pursue independently, given that it is all to do with aspects of my previous jobs and my own IP?