A guide to A-road Britain: A40

It might as well be said straight away: the A40 is not the prettiest road in Britain. It could not, like others we have chosen, fill a photo album with breathtaking views over moor or downland, and it could hardly be called underused, known to millions of motorists as the way out of London heading for the M40 to Oxford, Cheltenham, mid-Wales or the Midlands.

But it is a road of rivers, following the Wye, the Windrush and the Thames, whose path it roughly apes: both stream into London from far off in the Cotswolds, via Oxford and the Chilterns, reaching town tired and bloated after a long and varied journey. In London the A40 is an urban monster spread over six lanes, bisecting Acton and home to the Hoover building and countless self-storage units; but trace it back to its source and you'll find an important rural road, sprouting out of the agricultural town of Abergavenny, beneath the Black Mountains.

For me the London stretch is the road home, back to Oxford where I grew up, the beginning and end of a familiar traipse between the two cities. But west of Oxford is the A40 I love, a road that holds memories of setting off for camping holidays in the Forest of Dean, vintage car rallies in the Cotswolds and weekends and parties in the Herefordshire marches and Wales beyond.

Leaving Oxford you are immediately in David Cameron country, bypassing his constituency town of Witney to the right and the grey military planes of Brize Norton airfield on your left, familiar from so many news bulletins as the first patch of home to greet our early fallen heroes from Iraq and Afghanistan.

It's only once you reach the Minster Lovell roundabout, and the road narrows to a single carriageway, that the A40 hints at any bucolic charms: take a left through an undistinguished patch of wood and suddenly you emerge Narnia-like into the perfect English landscape overlooking the broad and dreamy Windrush valley that sweeps away to your right. This is Mitford territory, home to Asthall Manor, Swinbrook and the Duchess of Devonshire's family pub, The Swan, an ideal lunch stop whose walls are lined with sepia photographs of all her eccentric siblings. But we stay on the high road, hugging the valley rim as we press on to Burford, whose church spire pricks the horizon off to the right. Burford is one of those towns that turns perfectly normal Japanese and American people into zombies, and any day of the week you will find at least a coach load of them marauding down its steep high street in a trance of affecting wonder.

Happily the A40 hurries on over the top of town and soon we have swapped Oxfordshire for Gloucestershire. The Cotswolds proper are beginning, broad open fields becoming smaller and more frequently enclosed with dry stone walls. Road signs invite us off to the Rissingtons and the Barringtons (Little and Great), while on the main road we pass The Inn For All Seasons, for my money the best coaching inn on the road.

Soon the wrought iron gates and lodges of Sherborne Park have grandly emerged on the right, and if you have time you might peel off to visit the under-appreciated wool town of Northleach down a dark road to the left.

After the Northleach roundabout, frustrated motorists will use this stretch of straight road to overtake my dawdling Morris Minor, even though the patient will soon be rewarded with dual carriageway just round the corner. The A40 then passes through Cheltenham in a labyrinthine kind of way, so we cheat and deviate south and pick it up again north of Gloucester, having dropped steeply down into the Severn Valley. The network of roundabouts, sliproads and bypasses can get confusing here, but pay attention and you will see Gloucester Cathedral soaring over the town to your left. By now you are heading due west, straight for the southern end of the Malvern hills. Cathedral aside, this corner of Gloucestershire cannot boast exciting architecture or picturesque valleys, so we hasten on to Glasshouse Hill, and soon we are winding up through thick woods, hair-pinning right then left. It's a fun drive, demanding plenty of gear changing and good brakes.

Ten miles later and we are in Ross-on-Wye, an unpretentious but pretty border town that reminds you why you would never really want to live in the Cotswolds: there are no woollen jumper shops here or tins of biscuits costing a tenner. After Ross the A40 leaves behind the wooded chicanes and straightens out to shadow the course of the Wye over the Welsh border to Monmouth. From here it is a fast blast of dual carriageway to Abergavenny, the final call on this road. Beyond lie the hills of Wales, where the concept of an A-road is rather different altogether.