Circling the boundaries of Bentley Priory, a key wartime defence installation and still an important military base.
Distance 4 miles (6.4km)
Minimum time 2hrs
Ascent/gradient 197ft (60m)
Level of difficulty Medium
Paths Clearly marked footpaths
Landscape Mixture of pretty woodland trails and open fields
Suggested map aqua3 OS Explorer 173 London North
Start/finish TQ 158936; Stanmore tube 1½ miles (2.4km)
Dog friendliness No problems
Parking Car park off Warren Lane
Public toilets None on route
© AA Media Limited 2015. © Crown Copyright Licence number 100021153
1 From the car park turn right, along Warren Lane. At the junction cross the road and continue ahead along Priory Drive. Follow the road as it bends sharply to the right but, 50yds (43m) further on, go through a kissing gate on your left, signposted 'Bentley Way'. Continue along the track, with Bentley Priory to your right, and go through another kissing gate.
2 Where another path joins at right angles, carry on ahead (note that this is the path this circular walk returns along). The fenced area on the left is the deer park. At the end of the fencing ignore the path to the left but continue ahead as the track veers to the left, crosses a brook, and then reaches another kissing gate before emerging on to the common.
3 Continue ahead and, at a crossing of paths, turn sharp right across the common, along a waymarked path. This passes through a wood and then crosses a footbridge, to reach a row of houses. Bear right and follow this meandering, tree-lined track. When it joins a driveway leading to a farm continue towards a road ahead.
4 Turn right. Ignore the first footpath sign on the left and take the one along an enclosed path a few paces further on, just before Honeysuckle House. Follow this path. When it reaches the A409 turn right and take the first left into Brookshill Drive.
5 At the end of Brookshill Drive turn right past some buildings to Copse Farm, signposted 'Old Redding'. Follow this track then, at the T-junction, turn right. A few paces further on, go through the wooden gate on the left-hand side and continue walking ahead along this footpath through the wood. It swerves to the right of a gate and later runs along the side of Harrow Weald Common.
6 When the footpath reaches the end of the common turn right along 'Len's Avenue', so-named in memory of the park keeper who planted the trees here. When you get to the road turn left. After about 325yds (297m) cross over and pass through a large wooden gate. Go through a kissing gate and then along a footpath that bisects the common, with the grounds to the military base at Bentley Priory on your left-hand side, and Heriot's Wood down the hill to your right. Follow this footpath as it gently descends, before joining the outward path at Point 2. Retrace your steps back to the car park in Warren Lane.
By the spring of 1940, German forces had penetrated Western Europe so extensively that only Britain stood in the way of the Nazis taking complete control of the continent. It became clear, however, that Adolf Hitler was up against one of the best air forces in the world, and Bentley Priory played a strategic part in this battle of land - and wits.
Unlike the Royal Air Force airfields that were home to British fighter planes during the war, the land surrounding Bentley Priory was without aircraft, yet it was one of a number of such places that were vital to the success of RAF operations.
The former country mansion was taken over by the RAF in 1926. It was enlarged considerably before it became the headquarters of Fighter Command, a group of high-ranking officers and other personnel on whose shoulders rested the ultimate responsibility for defending the country. This elite unit was formed in 1936 as part of the RAF's reorganisation and expansion in Britain. It was further divided into a number of groups, each of which took responsibility for a particular region. At the beginning of the Battle of Britain, for example, London and the South East was covered by 11 Group. These groups were also sub-divided into geographical areas for additional precision.
Bentley Priory was the centre of a highly sophisticated control network that relayed information on hostile aircraft movements via secure landlines from the radar stations to its 'filter room'. Once the plots of hostile aircraft had been established, the relevant group was alerted and the sector stations then activated the fighter squadrons.
When, in 1940, German forces occupied the whole of the northern European seaboard, Britain braced itself for attack. The Luftwaffe knew that, to gain air superiority over southern England, it first needed to destroy the RAF's fighter planes. It was necessary to win control of the skies just long enough for land and sea forces to come ashore. The Battle of Britain, as it became known, ran from July to October. Initially the Luftwaffe attacked targets in the south, including radar stations, until it reached the airfields near to London in 11 Group. Sir Winston Churchill, who had become Prime Minister in May of that year, told the House of Commons that the battle of France was over and that he expected the battle of Britain to begin soon - it began one month after his remarks. The Battle of Britain was a close shave, with some of the vital airfields around London being struck, but the enemy made a tactical mistake in choosing to concentrate on the capital. A week later, Fighter Command had recovered sufficiently to prove its superior strength. Today, in peacetime, Bentley Priory remains important, monitoring the security of British airspace.
Grim's Dyke is a major earthwork some 4 miles (6.4km) long. It's best reached by turning left at The Case is Altered and taking the footpath on the opposite side of the road. Excavations in 1957 revealed that the apparent military boundary dating from the 5th century ad was built with only primitive wood and flint tools.
Where the track past Copse Farm to Old Redding meets the road, you'll find a pub with the unusual name of The Case is Altered. Some say it's derives from the Spanish 'casa alta' (high house) but others think it came about when judges used to meet here, discuss cases, and possibly change their minds. The food is creative but simple. Hand pumps include Old Speckled Hen and Calder's. The garden has a wonderful view over the surrounding countryside.
When you enter the wood at Point 5, look out for beech trees. They grow well in this easily drained, gravel soil and can reach a height of 130ft (40m). They are recognised by their smooth, grey bark, and long, pointed brown buds and oval-shaped leaves. Older beeches flower in May and drop their seeds in the autumn, providing a good supply of food for squirrels and birds.