Yes, it's a tricky one, that. Mention "own business" and expect bridges to get burnt to the ground. On the other hand, it sounds like they've pretty much fallen down already if the boss is that aggressive.Maybe you could plan a little preamble, without mentioning the business idea, and see how it goes. If you get both barrels, then a strategic retreat might be in order (it's difficult to know whether they would implement gardening leave to protect their interests or block it just to spite you, in which case a default position of staying out of harm's way probably isn't a bad idea!). If the reaction is better than expected, you could at that point potentially mention the business idea as an option you're considering and even suggest continuing to be business associates of some sort. I think however that, with a boss that aggressive, and also working in a business where personal relationships are so important, mentioning the business idea is just likely to lead to them trying to take action to cause problems for you. Even if you don't have any covenants, they'll possibly try and chuck hurdles in your way. Besides, if they don't give you gardening leave, then it gives you time to do some intensive self-marketing and networking under the guise of doing your day job! But definitely check that contract out... make sure you're on solid ground...