The Mail centre ignore the address when sorting and just go by the postcode. They will pass it on to the local Delivery Office for that Post Code.
On arrival at the DO, the parcel sorters will read the street name and pass it on to the "Duty" that covers that street. Or if it's covered by 2 or more they will check the postcode and pass it to the most likely duty.
By this time, it's down to local knowledge so if your regular postie recognises the name it will be delivered as normal. If they don't recognise the name they will hold on to it for a few days to try and match it to a letter with the same details.
But, the official line is that incomplete addresses should be returned to sender on arrival at the Delivery office.