New Build Supply Issue

Has anyone here had an issue getting a connection to a new build, due to a substation being at full capacity? We are building in a residential area, albeit rural and on a plot of land that did have a property on it, although some years ago and upon requesting a temporary supply, the surveyor has informed me that I will have to pay to upgrade the network. When I asked about costs he said it could be anywhere from £10k to £100k. Obviously in a bit of a panic and thought I’d reach out to you experts and see if anyone could advise or alleviate my fast beating heart rate!  Also, to ask if the old connection would have any bearing? Many thanks all.