Adverse Possession?

I am in the process of purchasing a property whereby the seller holds the freehold and leasehold titles of the house and 90% of the garden. However, on a section of the rear of the garden, there is only a leasehold title. Am I right in thinking the lessor should hold the freehold title. The lessor is now a dissolved company and there is no record held of the freehold. There is also no copy of the lease held with HMLR. In this case would adverse possession come in to play as the property has been like this since 1969?

Joel - it's either a case of adverse possession or lost deeds it seems - see PGs 4, 5 and 2 for appropriate guidance but please do speak to your conveyancer for advice as you clearly have a complex scenario to consider