The answer to your question lies in your council’s planning policies contained in its Local Plan. Basically, if your property lies within the built-up area of a town or larger village, then there’s a good chance you’ll be able to build. However, councils prescribe the areas where you can build on the maps in the Local Plan. Look these up on your council’s website, or call in at the planning department and have a look there. If you’re in an area where new housing is allowed, the next question is whether it can be accommodated satisfactorily without compromising the appearance of the area or the privacy of neighbours. To be on the safe side, check by asking a planning officer at the council, and, if it seems marginal, take professional advice from a planning consultant.