Thank you for your question. If you cannot trace the person with the benefit of the covenant to gain a release from the covenant then you should consider obtaining a restrictive covenant indemnity policy to cover the liability of the future breach of the covenant.
If you google "restrictive covenant indemnity insurance providers" you will be able to contact providers. They will need a copy of the restrictive covenant wording, the nature of the contemplated breach, the date the covenant was imposed and details of the steps you have taken in attempting to contact the person with the benefit of the covenants.
They are relatively cheap (usually less than £150.00) and the benefit of it can be passed on to your successors in title (people who buy the property from you). You will also need to contact your lender to gain approval of the insurance policy.
There is also the option of applying to the Lands Tribunal to either modify or discharge the covenant, but his is quite an expensive process and takes quite a long time.
Note this is completely separate to any planning permission/buildings regulations approval that you may need to obtain for the works.
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