Hi Wildgoatie
I have to deal with utility companies on a daily basis making applications for new supplies, etc. WPD are, without a doubt, the best utility company we deal with. The person who has completed your quote is an engineer who has sat down and most likely spent a great deal of time to find the most economical way of connecting you to the grid. As a utility company, they have a duty to provide the customer with the most economical way of connecting to the grid. From the additions you're making, it sounds like they may be upgrading part of their network, and the engineering time in that alone will be quite substantial.
Anyway, generally your quote sounds reasonable, although without a breakdown it's hard to say. It also sounds like they're installing a pole below HV overhead lines so an element of risk may have been priced into the works as it sounds quite dangerous.
As a side note (and this doesn't help you I understand), WPD prepare their quotes free of charge so it might have been better to contact them at the beginning of the job, before you started onsite.
You could look into a combined heat and power solution – go to the calor website for more details.