Where a joint owner dies, what determines if the survivor will need to pay inheritance tax is not whether you are joint tenants or tenants in common – rather, what's key is your relationship to the joint owner.
A key thing to remember is that assets such as property which pass between married and civil partnered couples are exempt from inheritance tax. This means, regardless of whether you were joint tenants or tenants in common, if ownership of the property passes to your spouse or civil partner then inheritance tax does not apply.
But this exemption does not apply to any other type of people, such as cohabiting couples.
So if you own a property with a partner you're cohabiting with and ownership passes to them, then inheritance tax might be due. Whether it is will depend on the value of the deceased's estate, including their share of the property, and if this exceeds the inheritance tax free threshold (currently £325,000).
Similarly, if ownership passes to a joint owner who is a friend, sibling, business partner, or to somebody who isn't a joint owner (and you're not married to them), inheritance tax might be due.
Inheritance tax is a complex topic. See our Inheritance tax to go through the basics (including how to boost your inheritance tax-free threshold to £500,000).