Hi Woofa012,
Whether or not you hold your property as joint tenants or tenants in common, the outcome will likely be the same. The law does not go very far in regulating rights between co-owners. Specifically whether or not your right to exclude a third party is a superior right to that of your co-owner to permit someone to visit the house is not established at law. There are only a few established principles that case law has provided which can give you some guidance, however the rest is up to the parties to come to an agreement on.
The main principles are that each co-owner of a property is entitled to use and occupy the entire property and must permit each other co-owner to do the same. If one co-owner uses the whole property, without attempting to exclude the other, the co-owner occupying the property does not have to pay any rent or occupation fee to the other co-owner. This would tend to indicate that you right to exclude is equal to your co-owner's right to permit someone to enter the property. Therefore unless there is some legal reason that you have for not allowing the person to enter the property - i.e. fear of apprehended violence or other, then its an issue you and your co-owner will have to resolve between yourselves.
