Yes, for most of the village. Hardly anything is listed. There is one conservation area. The neighbours are applying for planning permission all the time. In Smallfield, the thing most likely to stop an extension is the quote from the builder, not the council.
The wider area has 10 listed buildings: one Grade I, one Grade II* and eight Grade II. Listing covers the whole building, inside and out, so almost any change to one of those ten needs listed building consent on top of ordinary planning permission, and "like for like" becomes the only phrase the planning officer wants to hear. Ten buildings is a short list. Unless the house has a listing entry of its own, the heritage rules do not apply to it, and the chance of that across a village made mostly of post-war semis and bungalows is small.
There is one conservation area, Burstow. Inside it, the council takes a closer interest in what the street sees: demolition, some tree works and changes to front elevations can need consent that would not be needed elsewhere. No Article 4 directions are recorded here, so check with the council before assuming anything beyond the standard conservation-area rules. Outside Burstow, a house faces the ordinary process that every other suburban extension in Surrey goes through.
The planning register is busy. There were 2,460 applications between April 2024 and June 2026, and 1,089 of them in the last twelve months. Those figures cover the wider area around the village rather than Smallfield alone, but the message is plain: people here alter their homes, and do it often. A street where half the houses have already gone out the back makes it hard for anyone to claim that one more would ruin the character.
In practice, most of Smallfield is ordinary permitted-development territory. Many rear extensions, loft conversions and outbuildings on an unlisted house outside the conservation area can go ahead without a full application, within the national size limits, though a lawful development certificate is cheap insurance when the time comes to sell. A listed building or a site in Burstow needs a proper application from the start. Check the exact address against the council's planning map before sketching anything, because the one house on the street with a history is always the one someone has just fallen in love with.
Smallfield is one of the easier places to add a room: little listed stock, one conservation area, and a planning register that shows the neighbours doing exactly what you have in mind.