Metropolitan Line and
Network Rail boundary position

and the Mantles Wood myth


The boundary between the London Underground and Network Rail systems north of Amersham is often referred to as being at Mantles Wood. This is not the location of the boundary, it has never been the boundary and furthermore it isn’t even very close. I have not been able to discover who first perpetrated this myth, or why it is so widely and uncritically accepted, but it seems that it is a myth that needs exposing and correcting. My first indication of wrong use of name goes back to 1950s.

Two questions arise. The first is where is the boundary? The second is where is Mantles Wood in relation to that boundary?

Property boundary

Historically, the whole of the railway between Baker Street and the junction immediately south of Aylesbury was owned by the Metropolitan Railway (Aylesbury station was owned jointly with the Great Western). The question of a property boundary in the Amersham area did not, therefore, arise.

When British Railways (BR) took over all services north of Amersham they also took ownership of the associated track and it was necessary to fix the position where ownership changed. The section Great Missenden-Aylesbury South junction was transferred from LT to BR (London Midland Region) from Monday 11 September 1961. The property boundary was defined as a point 1000ft north of the Up Distant signal (RJW1) north of Amersham.

Up home signal JW1 is located 682ft north of milepost (MP) 24¼, and RJW1 3486ft north of that. Adding 1000ft more (as indicated by definition above) puts the boundary a distance of 5168 ft [78ch] north of milepost 24¼. In turn this places the boundary at 25m 18ch, just south of MP 25¼ (the exact position defined as 25 miles 400 yards). As a point of reference, Amersham station was centred at 23miles 66ch, or near MP 23¾, making the boundary about 1.4 miles north of the station. Mileposts state distance from south ends of platforms at Baker Street.

This boundary has not moved. The current London Underground boundary map clearly shows the boundary just south of MP 25¼, noting it is 30 metres away (a poor rounding of 40 yards). Topographically the boundary is at the north end of a short embankment and almost exactly coincides with the boundary between High Spring and Ostlers’ Wood, both on south side of the line. OS grid reference is SU944989. Current instructions recite that the boundary is at 87.077km (irritatingly adding that it is at Mantles Wood). MP 25¼ remains the Network Rail reference point but the LU network is now referenced metrically, and the milepost reference is stated to be at 87.114km. This indicates the property boundary is 37 metres south (converting to 40 yards and confirming position as 25 miles 400 yards).

Although the terms north and south are used, the line actually runs nearly west-east at this point, so in topographical terms references to ‘north of’ need to be understood as meaning ‘west of’ (and so on).

Mantles Wood

Before worrying about what the railway calls places, it is first necessary to identify where Mantles Wood itself is located. Large scale maps show this to be a little to the west of Mantles Farm, and situated on the north side of the railway centred at OS grid reference SU918996 (OS 50,000 map marks Mantles Farm). The railway at that point is on a slight embankment. The wood occupies much of the distance between MP 26¾ and the footbridge (bridge MR119 [Mantles Farm] on footpaths linking Little Missenden Church with the public house at Hyde Heath and Middlegrove Farm).

We now turn to the railway’s interest in this place. Because of the distance between Amersham and Great Missenden an intermediate signal box was provided along this section in 1900. The name of the box was Mantles Wood and it was provided with block signals but no pointwork. The box was abolished in 1924, at which time the signals were converted to electric control as extreme advance starters (still semaphore) from Amersham and Great Missenden boxes; they appear to have retained their original positions. At the same time their distants were converted to automatic repeaters; these were a very long way from the signals repeated, over 4000 ft in both cases. The Mantles Wood intermediate block signals were converted from semaphore to coloured light during Thursday 12 June 1952. At that time the northbound signal was Amersham No 24 with its repeater and the southbound signal was Great Missenden No 5 and its repeater.

Contemporary maps (for example 1:2500 of 1925) indicate the signalbox had been immediately west of the footbridge (referred to above) on south side of the line. Grid reference was SU921993. Metropolitan Railway documentation places this signal box 2m 64ch north of Amersham. Since Amersham station was located at 23m 66ch this places Mantles Wood box at 26m 50ch (half way between MPs at 26½ and 26¾).

On the face of it this places the site of Mantles Wood box and adjacent overbridge MR119 some mile and a half from the present LU/Network Rail property boundary.

Other Information

The new signal box and IMR at Amersham came into use on Sunday 20 March 1960. The Mantles Wood signals were retained, but the up (southbound) signal (Great Missenden No 5) became automatic and was renumbered A983. Its repeater became R983. The northbound signal (Amersham No 24) became Great Missenden No 30, and its repeater R30. These signals (of LT pattern) retained their traditional location near the old Mantles Wood signalbox but were removed during the British Rail Chiltern Line resignalling of 1990. Signal A983 had been 8822ft from RJW1, putting the actual boundary 7712ft from the property boundary (confirming nearly 1½miles).

After the transfer of the line to BR, LT continued to undertake civil engineering and track maintenance (but not signalling) on its behalf for some years. From 1967, BR undertook all the work itself. For some maintenance purposes boundaries were fixed that were different from the property boundary. Network Rail track maintenance therefore begins at MP25¼ while signal maintenance on the southbound (or up) line begins 30 metres to the south of MP 25¼ (just north of the property boundary). On the northbound line Network Rail signal maintenance begins 413 metres (1355 ft) north of signal JW70 (this is roughly 60 metres south of MP 25).

The route of the new HS2 railway crosses beneath the former Metropolitan Line (in tunnel) north of the Network Rail property boundary, about half way between the boundary and Mantles Wood footbridge.

By the way, the actual woodland called Mantles Wood comprises 7¼ acres of beech woodland and was recently changed hands for £59,000. It is described as semi-natural ancient woodland and is in the Chilterns Area of Outstanding Natural Beauty.


The evidence indicates that 'Mantles Wood' was a signalbox (and subsequently a colour light signal) location half way between MPs 26½ and 26¾, by bridge MR119. The property boundary, despite abundant misinformation, is near MP 25¼ and about a 1½ miles away. Contextually, Mantles Wood is more than twice the distance from Amersham as the actual boundary point.

In today's metric measurement scheme the sequence (running north) is Amersham station 84.85km, property boundary 87.08km and Mantles Wood 89.33km.

If the boundary point has to have a name, then 'Weedonhill Wood' probably fits the bill. This wood runs along the northern edge of the railway and its western boundary coincides closely with the railway property boundary; the name has the merit of being shown on 1:50,000 OS maps. If this is unsuitable then High Spring, the next named property to the west, might be suitable (and is shown on OS 1:25,000 maps). But not Mantles Wood.

Location Map

A map of the area discussed above may be found by clicking here: The property boundary is approximately in the centre, where the orange arrow is situated. Mantles Wood is at the left hand edge, to the left of the footbridge underneath Mantles Farm. Amersham station is to the right (probably off map depending on screen settings).

There is a photograph of the boundary sign on the web (apparently a London Underground production), and this is taken from the LU side looking west. It may be found here (due courtesy to the Railway Eye). You can click on photo to enlarge it. As already stated above, it may say it is Mantles Wood, but the wood is over a mile farther on; just visible in background is MP25¼.

Does it Matter?

Well, in the great scheme of things — no!

I offer this up mainly because the information is to hand and it may as well be out there in cyberspace as not. Historians may find it helpful.

I would just make a mild observation that not naming places correctly can lead to problems, quite apart from being bad practice. Were an accident to occur, for example, there is a risk of people being sent to the wrong place and causing a delay. A mile and a half is quite a long way to be wrong (at least 20-25 mins walk). Perhaps it would be easier to rename the wood.