I'm a bit surprised such wording was used so recently - reference to coach houses & stables is generally indicative of an older era.
However, either the covenants were carried over from much older documents or someone who could benefit from them was around in the 1930s. (If the original house on your site was built in the 1930s & simply replaced in 1979 then the same clause would remain - it applies to the land rather than being specific to the house.)
Often these covenants are stated in the deed to be for the benefit of someone or some organisation. For example, for the benefit of whoever owns the neighbouring land. If there is anything like this in the deeds then whoever is now the relevant landowner could probably raise an objection to what is proposed.