"bigbrian" wrote
| My question is is this something that the surveyor should have
| anticipated when the project was specified,

He should have anticipated that it is *possible* that there *may* be a
soakaway.

| The contract doesn't seem to make any specific mention either way
| of reserving the right to charge me extra for unforeseen problems
| in the building element of the job

Depends on whether the contract says, and the price was for, "erect a
conservatory" or "do all works necessary to erect a conservatory".

Owain