HS2 Update, December 2021

HS2 Update, December 2021

On the 18th of November, the Government announced its decision to scrap the Eastern leg of HS2 which would have connected an East Midlands Hub to Leeds.

The Eastern leg represented a key government justification for building HS2, on the basis that it would help bridge the north-south divide. However, this retrenchment, and increasing concern over spiralling costs – including the House of Commons Public Accounts Committee being “increasingly alarmed” about key elements of the programme – the business case for the whole route is on even shakier ground.

However, for the Chilterns, the HS2 proposals still roll on and continue to gather momentum.

Chalfont St Peter Vent Shaft

The first of the huge Tunnel Boring Machines (TBM) will reach Chalfont St Peter in December and break through into the base of the Chalfont St Peter vent shaft shortly after Christmas.  Meanwhile, we remain concerned about the potential damage to the aquifer and our rare chalk streams, particularly considering the TBMs will mine at a shallow depth beneath the River Misbourne at Chalfont St Giles (possibly as early as February next year) then beneath the top end of Shardeloes Lake, near Amersham, later in the year.

Bacombe Hill and Wendover

We have also raised concerns that construction of the cut and cover tunnel through Bacombe Hill will disrupt water flow to the Wendover Springs, which in turn flow onto the Wendover Arm of the Grand Union Canal and the Weston Turville Reservoir SSSI. At the November meeting of the Chilterns Review Group, we were informed by EKFB (the designers for this section of the route) that issues concerning drainage of the HS2 route and impacts on the SSSI were being considered.


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Looking South from Wendover Dean to South Heath, Nov 21. The Chiltern Society HS2 photo diary.

Preparation for the main cutting running north from South Heath towards Wendover is now underway with topsoil stripping and further hedgerows and trees being removed.  The main cutting excavation will take place through summer of 2022 with hundreds of thousands of tonnes of spoil being carried along the new construction road  to a ‘temporary’ storage site.

The Oak Trees of Leather Lane

Earlier in the year, along with others, we raised concerns about revised plans for the Leather Lane diversion which would have led to wholesale removal of over 50 mature oak trees beside the existing lane.  We are pleased that the contractors, EKFB, have been able to reconsider their designs and, we are told, a significant number of trees will be saved.  Final numbers of trees lost and saved are yet to be confirmed.

Grims Ditch and Small Dean Viaduct

We continue to engage with Natural England, the Independent Design Panel and Buckinghamshire Council to provide advice on developing designs including vent shaft headhouses, overbridges and new road design, noise barriers and landscape mitigation.  We understand that the Schedule 17 planning applications for Bowood Lane, Grim’s Ditch Scheduled Monument and the Small Dean Viaduct will be submitted to Buckinghamshire Council planners in the new year.

Risks to the Chalk Aquifer

A major pollution incident at the Chalfont St. Peter vent shaft came to light following a Freedom of Information Request by members of the Misbourne Protection Group in August 2021. HS2’s contractors, Align, reported the ‘loss’ of 2,400m3 of bentonite clay into the aquifer between August and November 2020 during construction of the vent shaft. This bentonite was reported to have been detected in groundwater 500m from the site.

In May 2021, after attempts over a number of years to secure assurances, the CCB and Buckinghamshire Council set out their shared concerns and a series of questions for HS2 Ltd regarding the impact of the tunnelling on the chalk aquifer. So too did a group of NGOs led by the Chiltern Society, which also developed a briefing on the risks to the chalk aquifer and to the Chilterns chalk stream from its Geological Advisor, Dr Haydon Bailey, a Chartered Geologist who specialises in chalk geology. Despite the confidence of HS2 Ltd and its contractors, they have still failed to satisfactorily answer our questions.

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Amersham Vent Shaft looking north, July 2021. Image: The Chiltern Society.

Amersham Vent Shaft Headhouse dubbed the 'crown of thorns'

  • Designs for the Amersham Vent Shaft Headhouse incorporating anodised aluminium fins have been dubbed locally as the ‘crown of thorns’.
  • Originally it was suggested that the site (adjacent to the A413/A404 junction on the edge of old Amersham) required an artistic or architectural statement for the design of this headhouse structure due to the ‘visibility’ of the site being considered to prevent the normal design approach of ‘maximum concealment’.
  • A design was developed that employed a semi-transparent circular crown of metallic fins, angled to emulate the slopes of surrounding hills and reflect the sky, creating a dynamic appearance when viewed from a moving vehicle. We expressed concerns about the size of this feature, the materials used and the proposal (at one time) for illumination at night, but the overall idea was favoured by the Independent Design Panel and by Bucks Council officers.
  • Over time the designers adjusted their expectations of the necessary size of the structures and associated compound and have made changes to the level of the site to accommodate vehicle access.
  • These changes have been so effective as to render the compound and the vent shaft structures themselves almost invisible. Only the artistic aluminium crown was widely visible, and ‘windows’ needed to be left in the surrounding belt of trees in order for the structure to be enjoyed as intended by passing motorists.
  • Our planner, Matt Thomson has argued that the rationale for an artistic/architectural statement does not apply if the structure can be rendered almost invisible. The designers have so far failed to respond to requests to provide visualisations of the structures without the ‘crown of thorns’ in place and have continued to defend their design ‘narrative’ even though the design fails to meet the specific criteria in the agreed Detailed Design Principles.
  • The schedule 17 application is now being considered, and we have continued to press for practical measures such as increased vegetation screening and removal of the fins which would largely remove the visual impact. We await the outcome of the application with interest.

We will continue working to encourage contractors to meet their own environmental standards, reduce harm and seek what improvements we can to emerging designs.


The Chilterns Conservation Board has been involved in the High Speed 2 (HS2) project extensively since it was first announced in 2010 and together with many other local groups and individuals, argued that the route should not pass through the protected landscape of the Chilterns AONB.

Although the Chilterns Conservation Board remains steadfast in its view that HS2 will have a significant and lasting negative impact on the Chilterns Area of Outstanding Natural Beauty, it continues to work with the HS2 Review Group and relevant partners to secure the best possible outcome for the environment despite the decision. Read more about our work over the last ten years via the link below:

Related news

HS2: more sinkholes open up in the Chilterns

We are aware of a further two sinkholes appearing in farmed fields between Sibley’s Coppice and Frith Hill.

Hyde Heath Sinkhole

We have been made aware of a second sinkhole occurring above one of the HS2 tunnel boring machines (TBMs) in Hyde Heath.

Chilterns Conservation Board’s position on the cancellation of the Northern Leg of High Speed 2

The announcement by the Prime Minister cancelling HS2 north of Birmingham undermines the justification for the remaining section of the route.


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The Management Plan for the Chilterns National Landscape

The Management Plan sets out the policies and actions to be followed by all stakeholders to conserve and enhance this special place. The current Plan (“the Chilterns AONB Management Plan 2019-24”) has been extended to March 2025 and is currently under review.
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Plan your trip to the Chilterns!

Search the interactive map: select from a list of categories to bring up icons showing the location and information of walks, bike rides, places to visit, tasty local products and plenty more across the Chilterns area