In the general case, when a company is dissolved any assets still belonging to it becomes bona vacantia under Section 1012 of the Companies Act 2006 which means that it belongs to the Crown.
The Crown can then choose to disclaim its rights to the asset under Section 1013, and typically will do this where there are risks involved (e.g. leasehold land). The effect of dislaimer, per Sections 1014 and 1015 is that the "property is deemed not to have vested in the Crown" and it terminates "the rights, interests and liabilities of the company in or in respect of the property disclaimed".
In the case of freehold land that is disclaimed, it escheats (transfers) to the Crown Estate and the freehold interest is extinguished. According to Practical Law (paywall):
Note, if the land is registered, the registered title will remain and
the Land Registrar may enter a notice on the Land Registry title if
notified (rule 173, Land Registration Rules 2003). The notice will
recite the fact of the liquidator's disclaimer or Crown disclaimer but
will not otherwise specify that the land has passed by escheat.
The Crown Estate then becomes entitled (but not obliged) to take
possession of it. The Crown Estate will not assume any liabilities as
owner of the land unless it does take possession or exercises control
over the property. The result of this is that the only action the
Crown Estate will generally take as regards escheated land is to sell
the whole of the land to a suitable buyer who approaches the Crown
You can read more about how the Crown Estate subsequently deals with such property (including if and how it sells the property) in their FAQs.