If you are buying jointly with someone else, you will need to state in the transfer document whether you wish to hold the property as tenants in common or as beneficial joint tenants.
If you choose a beneficial joint tenancy, you own the property equally and on the death of one of you that person’s share passes automatically to the survivor.
Alternatively, tenants in common can hold the property in unequal shares and their share passes under the terms of their Will or under the rules of intestacy if there is no Will.
Finally, in some cases it may be possible to access the property between exchange and completion, for example, if the property is empty, provided the seller agrees and provided you enter into a key undertaking. Discuss this with your solicitor.