There is no need to worry.
There is a registered system in place for conveyancing, which replaced the old style unregistered system whereby a Seller would hold the physical deeds to the property. When a property is sold now it is automatically registered at the Land Registry and you receive Land Registry Official Copies as evidence of your title, the relevant details of the old conveyances (ie. the deeds) are noted on the Official Copies by the LR and then dematerialised (destroyed).
The original lease relating to your property would also have been taken and held by the LR and copies of it can be ordered. If you have a copy of it (ie. Lease of Part) then you should pass this to your conveyancer to save them having to pay the LR a fee to download a copy. This together with the OC's confirms your title to the property.
I assume OCs in your possession are fairly old so that Buyer will request that new ones are ordered at a cost of £16.00 total for new OCs and the associated filed plans.
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