The interior of Mallards Cottage where Georgie Pillson lived (in the BBC adaption) used The House With Two Front Doors in Mermaid Street. For the exterior of Mallards Cottage in the recent BBC series, Lamb Cottage was used. This was also the location of Mallards Cottage in the books.
Channel 4 used 29 Watchbell Street in their 80’s production.
The House with Two Front Doors