If your home is mortgaged, strictly speaking you should also inform them too, but having let rooms before, you need get no other insurance as strictly speaking that is down to them. However, for your own insurance needs (basically covering yourself) you must disclose that you have a lodger. Failure to do so could invalidate any claim you make.
Be advised they might want details of the lodger, or rimpose restrictions and/or efuse to cover if the person concerned has a dodgy background.