The answer is maybe... I work as a planning officer and it comes as a shock to a lot of people with grass verges around their land to find that parts of their plot are designated as Highway as they have utilities under them and even though the land forms part of the house plot, the owner cannot build on them without the Highway Authority's permission and if there are utilities under them the homeowner has to pay to relocate the utilities etc. So applying this logic to your case, it may well be that there are utilities under your land but the Local Authority has a charge over the land to access the utilities - therefore yes they can access them but its pretty bad practice not to warn you.