I am sure that no advice can be provided based on the information given. What's this new business? Microsoft? The corner shop?
Generally speaking 3% ownership doesn't mean much in any business because it is unlikely that you will have a say in the way the business in managed.
However, if the business is able to generate a return that is higher than what you would get on a stock market or from a bank deposit, then yes, the investment can be a good thing.
Does the business fall under Enterprise Investment Scheme? If yes, then you may get tax relief.
Speaking on tax, you may have CGT and potentially IHT issues when you want to dispose of your interest if your spouse is also a shareholder, etc.