Legal 'due diligence' - checking that the landlord has the right to sell the lease, investigating planning decisions and so on - can take several weeks. The whole process can be more complicated and drawn out if several parties are involved (when, for example, the landlord is also a tenant of another 'superior' landlord).
If appropriate, you may want to negotiate a 'lockout agreement' with the landlord. This prohibits the landlord from negotiating with other prospective tenants or accepting any other offer provided that you exchange contracts within a set time limit. owever, this does not compel the landlord to exchange contracts with you during the "exclusivity period", it only prevents the landlord from dealing with other prospective tenants during that time.
