* At the time you pay the £250 (*), you are placing a conditional order for installation of service
* The survey goes ahead, and you are told what the confirmed cost will be
* From that point you have 30 days to pay the balance to proceed (**)
* If you don't, the order is cancelled and the £250 is non-refundable
* If you place an order again later, the whole process starts from the top. You pay the £250 again, and the confirmed cost could be lower or higher.
(*) You pay this to the service provider. They in turn pay the
Openreach survey and design charge of £244.52 if the order does not proceed.
(**) It's unclear to me if this money is paid immediately to Openreach at this stage, or if the service provider sits on it until completion.