Not usually, but it depends on the nature of your work. There's normally no need to inform your insurer if you're doing clerical work, such as working on a laptop and making calls.
However, if you have visitors to your home who are there as part of your work, or you have stock you've brought home (for example, if you've a mail order business which you're now operating from home), those won't be covered. If either of these apply, you'll need to check if you can pay a premium to have the visitors/stock covered, or you may need to get an extension to your usual business insurance.