We found a 3 bed terraced ex-council house with a garden for £420k. It doesn't have any dedicated off-street parking and instead shares parking bay spaces with other nearby ex-council houses. The garden also is next to a tube line (running every 3 mins). We can't hear the tube when inside the house but can hear it when in the garden.
As comparables we found other similar 3 bed terraced or end of terrace houses (that are not ex-council) nearby with dedicated off-street parking spaces for about £450k.
Given the fact that the above house is ex-council, doesn't have dedicated off-street parking, and has a tube line running next to the garden, what can be a reasonable discount to expect relative to these comparables?