Where a public highway is adopted, will this allow adjoining owners to arrange for services to be laid in the highway?

My developer client is building out a residential housing scheme. Our highways search shows that the road adjoining the site is adopted and maintainable at public expense. Our land registry enquiries show that the subsoil is registered and owned by a company entity (not the local authority). Our client has arranged for services to benefit the scheme to be installed within the adopted highway. The owners of the subsoil are claiming that the installation of services is a trespass and that they are entitled to compensation. I am therefore investigating the extent of the vesting/ownership of land and associated rights. I note the wording of section 263 of the Highways Act 1980. Upon reviewing your Practice note, Highway maintenance responsibilities of a highway authority, I also note the following statement: “The highway authority's interest extends into the subsoil beneath the surface of the highway, and into the airspace above the highway, but only to the extent required for the exercise of its powers and the performance of its statutory duties.” Given the usual drainage etc that would occupy a certain depth of land/road, the above statement would suggest that ownership vests in the local authority of sufficient land to allow such other services to be installed within the adopted highway and for there to be no trespass against a private owner of the subsoil. Please would you confirm the source of the statement so that I can independently verify the same, as I cannot trace such wording within the Highways Act 1980, but do appreciate that case law and other legislation shall also apply.