Single stage means Openreach expect to get your service in with a single visit , somewhat strangely though that’s not the norm when the survey notice states a potential problem ‘congested duct’.
From the early 1990’s the standard BT ( as it was then ) service method for houses was a fully ducted route so if your house was built after then , there will be a duct , but there was something that caused the surveyor to indicate a potential problem…if your house was build in the 1960’s up-to the early 1990’s , its an underground service but not fully ducted method, in those cases excavation is to be expected but the surveyor note is different, it would say ‘partial DIG’ , but it’s possible the surveyor has used congested duct incorrectly, or there has been a change in policy to use that survey marker ( I’m not as upto date as I once was )
No need to get hung up on priority exchange, that’s just where copper products can be ordered at all , as FTTP is available and is the default once it is available, it’s an irrelevance.
Most underground services are from the front , from joint boxes in the footpath , excavating may be necessary should the existing duct be blocked but they would obviously ask before digging in your land , if the blockage was in the footpath, they obviously dont need your permission but there is no need to worry until it’s established if the duct is OK or not , it’s only a suspicion that its ‘congested’
