Yes, you can, but you need to make sure that your employes knows about it. You may have a clause in your work-contract, that would require approval for your sole-trader activity. Even if you don’t have such a clause in your work contract, it would be the ethical thing to do to let your employer know.
Best of all, many of my current clients actually started out by having their employer give them the first order for their new business.
Remember small business is all about relationships, trust (even in this cynical world) and networking. ST.
Disclaimer: As with any of my readers questions, I do not have all the answers and here on my blog I can only give you some ideas, since I know very little about your small business. If any of you can add anything here do so for the benefit of my reader, who asked the question and everybody else, leave a comment below – I’d be most grateful.