This is a very well hidden walled garden that’s very easy to walk past without noticing it’s there, and is home to one of London’s oldest trees.

The walled garden is about halfway between Southgate and Arnos Grove tube stations on the Piccadilly line and is a surviving remnant from an old manorial estate when all around here was empty fields.

The estate was part of Minchenden Hall, which was built in the 1740s by John Nicholl, but he died just after it was finished so never got to enjoy the house. His daughter inherited it and she married the future Duke of Chandos, who already had an estate not far away in Stanmore.

The couple died childless and the estate was left to the Mareques of Buckingham who wasn’t interested in the house and left it to ruin until it was demolished in 1853. The estate was sold off in the 1930s for housing, and that’s what fills most of the area now – leaving just this little walled garden next to the parish church.

Part of the reason the garden was created is the oak tree that stands in the middle – the Minchenden Oak, which is thought to be one of the oldest trees in modern day London.

The tree is thought to be 800 years old and a survivor of the ancient Forest of Middlesex.

In 1873 Edward Walford described it as having the largest canopy of any tree in England at 126 feet in diameter and “still growing”. A couple of decades later it lost some limbs in a storm, but still boasted a canopy of 136 feet (41 m) in spread.

Using the internation standard for measuring things, four double deckers could line up underneath its branches. Or two blue whales.

The tree canopy is rather smaller these days though as it’s elderly and with rot discovered inside the main trunk in 2013, the canopy was cut back to reduce the weight. The timber was reused in the pocket park though, for the park benches. To insure against a future loss of the oak, a sapling grown from one of its acorns was planted in May 2015, at the same time as some restoration work was carried out on the rest of the park.

Entry to the park is through a narrow gap in the wall onto the main road that’s totally unsignposted and really quite easy to walk past without noticing.

Inside, it’s a mix of flat lawn, some raised beds along the roadside wall, and plenty of trees that anywhere else would be the dominant feature, but here, mere striplings to the old man in the middle.

There’s a sunken area to one side that might either be a drained pond or an empty sunken garden. Dotted around the modern stone paving and mini-walls are a few pieces of decently carved stone, which are remnants from the former 17th-century Weld Chapel that was attached to the church next door.

A fence surrounds the Minchenden Oak to keep causal damage to the tree, along with a display board telling its history.

It’s quite a large, and on my visit, totally quiet garden, which anywhere else would likely be very busy, but it’s in a fairly residential part of London with little other than local residents and the local school for regular users.

So the venerable Minchenden Oak might be a bit lonely. You should pay it a visit.