buying a house with tenants living there with out a lease

Hi all,

i'm looking to buy a property they have tenants living there who aren't on a lease as in theres no lease agreement at all. they have been there for 8 years and apparently are really good tenants (the REA says)

if i purchase it i'd want the tenants on a written lease. my question is should i get a written lease agreement before going unconditional? i'm worried that the tenants wont sign a lease once i buy it and it could be messy.

or is this just a common thing?

cheers

buying a house with tenants living there with out a lease