How to decorate a 300-year-old farmhouse

The tumbling globes of white hydrangeas that frame the exterior of this pretty farmhouse give the first hints of the philosophy of interior designer Sarah Vanrenen: that of working with rather than against what already exists, adding comfort and style without outwardly appearing to have changed much.

When she married three years ago, she came to live at the Wiltshire farm where her husband Grant had always lived. 'This house, which dates from about 300 years ago, had been lived in by his grandmother. It was pretty, but also pretty rundown. There was potential, but it needed a lot of TLC.' All of which made it a perfect project for an interior designer.

Traditional farmhouses such as this can often, over the years, grow like Topsy - a bit here, a bit there, all added without control or much long-term intention. Although this scattergun approach can give a house a certain quirky charm, it can also render it inconvenient and awkward.

Take the kitchen, which today is large and comfortable with plenty of space for family life. 'It was almost uninhabitable and half the size it is now,' Sarah explains. 'Where the sink is now was the outside wall of the house and there was no access on the other side of the room to the field behind the house - only a glimpse of green through a small window.' This was, in fact, the one area where change really was needed, so with the help of architect Julian Taylor, the outside wall was demolished and rebuilt further out into the yard.

The new configuration also meant that a small, detached cottage in the yard could then be connected to the kitchen, to create a den for Sarah's two stepsons. It also meant that a porch and entrance hall could be built to replace the original narrow passage hall, as well as Sarah's pride and joy - a boot room, ordered and neat, and lined above and below the bench with old French fruit crates for storage.

The hall leads into a study painted bright yellow from Papers and Paints - a shade that Sarah calls 'double yellow line' - in which there is a high-backed sofa inherited by Grant. Rather than re-upholstering it, Sarah has draped it with as many throws and blankets as it will hold - four at the last count.

Beyond the kitchen is the dining room - once a 'very dreary and depressing' dark burgundy, now a bold chartreuse. It is hung with generous printed linen curtains. The choice of colour in this room, as in the yellow study and the peacock-blue walls in the kitchen, all illustrate one of the most attractive aspects of the house. Bored with a one-size-fits-all neutral palette, Sarah has used a wide range of colours. There are few primaries or pastels, but instead raspberry, lime, lilac and jade. 'I like it all to be surprising, a bit loud and edgy; in a non-symmetrical house that will never be grand, strange colours make it quirky and fun instead.'

The dining room and study both lead into the comfortable drawing room - more restrained in terms of colour, but warm and welcoming. Textiles are used generously on tables as well as on chairs, sofas and cushions, all lit by distinctive lamps and unusual, very pretty lampshades. Indeed, throughout the house, the lampshades call out for attention - unsurprising, given the fact that Sarah's mother is the interior and textile designer Penny Morrison. Her company Irving & Morrison sells a range of one-off lampshades, cushions and textiles. Some of Penny's shades are here, as are others made by Sarah from collected textiles and sari fabrics. 'Lampshades make a house feel really cosy, and if you don't have a lot of money to spend in one go, they are the things to get first to make an instant difference.'

Upstairs, the seven bedrooms are equally individual - one has a cheerful mixture of lilac and jade, another lime and sherbet pink. The main bedroom is a cool and pretty space - a false ceiling was removed to reveal the beamed vault above and the windows were hung with linen from Penny Morrison. Sarah has now also launched her own fabric range, a collection of bright, clear designs.

A visit to this house is instructive on so many levels: to take bold decisions at an early stage; to use colour to turn the normal into the notable; to mix patterns and styles together; and, above all, to never underestimate the power of a good lampshade.

Sarah Vanrenen: 020-7371 8465; vanrenendesigns.com. Sarah's fabrics are sold through Penny Morrison; pennymorrison.com