Hertsmere councillors deferred a 200MW data centre on the former Mercure Hotel site near Watford. They want answers on water, building height and payments.
A decision on a data centre campus at the former Mercure Hotel, on the A41 just outside Watford, has been put off. Hertsmere Borough Council’s planning committee voted on Thursday 5 November to defer the application rather than approve it, against its officers’ advice.
Councillors want written word from Affinity Water that it can supply the site, more on the height and design of the buildings, and talks on a bigger payment from the developer. The vote came at the end of an item that ran for more than an hour and a half, according to the council’s webcast of the meeting.
The site sits on the corner of the A41 North Western Avenue and Sandy Lane, about a mile south-east of M1 junction 5. It is in Hertsmere’s Bushey St James ward, not in Watford borough, but the hotel always traded under the Watford name and the plans are filed as “Tylers Way, Watford”.
What Ark wants to build
The applicant is Ark Estates 5 Ltd, part of Ark Data Centres of Corsham, Wiltshire. Application 25/1781/FUL covers about 7.3 hectares of Green Belt, including the hotel, a vacant house at 1-2 Burn Close and woodland.
The officers’ report sets out:
- four data centre buildings of five floors, up to 36.25 metres tall including screened rooftop plant
- about 200 megawatts of computing capacity
- two electricity substations, each up to 11 metres
- a five-storey visitor reception building of up to 20 metres at the A41 entrance
- 119 car parking spaces and 144 cycle spaces
- the main entrance off the A41, with emergency-only access from Sandy Lane
Backup generators sit inside each building and would be tested regularly. The report says Ark intends to run them on hydrotreated vegetable oil rather than diesel “wherever possible”.
The traveller site next door
Directly to the north is the Sandy Lane Caravan Park. The report describes it as a designated Gypsy and Traveller site with 27 permanent pitches, separated from the hotel land by the Hilfield Brook.
The council’s own urban design officer was blunt. The buildings “will have a significant overbearing presence when viewed from the adjacent caravan site”, the officer wrote, and the homes there “are typically poorly insulated against noise intrusion”.
The daylight study looked at eight caravans and chalets facing the site. With the existing tree belt left in place, 17 of their 52 assessed windows would fall below the Building Research Establishment’s daylight targets. Officers counted that as harm to neighbours and gave it “moderate” weight.
GATE Herts, the county’s Gypsy and Traveller charity, objected in February. It raised noise, dust, traffic, lighting and the bulk of the buildings, and asked the council to weigh the effects under the Equality Act. Officers concluded the development would not breach the council’s equality duty. Hertfordshire County Council’s Gypsy and Traveller liaison service was consulted and did not comment, the report says.
The update sheet issued before the meeting adds that generator testing could lift noise up to 7 decibels above background levels. Officers said that stays within the accepted limit for routine testing, which is 10 decibels.
On Thursday, Councillor David Lambert said the residents were being given “far too little account”. “I think we’d be sort of saying, well, okay, it only affects 35 windows out of 53,” he said. “I think that’s not enough to justify putting something like this beside where people live.” He proposed the deferral.
Another committee member said the caravans “are homes” and “should be treated the same as houses”.
The objections, and the officers’ case
The council received 1,190 public comments: 1,184 against, four in support and two neutral. Aldenham Parish Council, the Letchmore Heath Village Trust, the Patchetts Green Residents Association, the Radlett Society and Green Belt Association, and the Hertfordshire and Middlesex Wildlife Trust all objected.
Their main points were Green Belt harm, the height of the buildings, noise, water and power use, the loss of a small fragment of ancient woodland, and a construction period the report puts at ten years.
Officers recommended approval all the same. They judged the land to be “grey belt”, meaning the scheme does not count as inappropriate Green Belt development. They also gave “very significant” weight to the national need for data centres and the lack of other sites. The land is already allocated for employment use in Hertsmere’s draft Local Plan.
The report also lists the economic case, using Ark’s own estimates:
| What | Applicant’s estimate |
|---|---|
| Construction jobs | 470, over about ten years |
| Permanent jobs | 255 |
| Economic output (GVA) | about £372m a year |
| Business rates | £19.2m |
At the meeting, Ark’s chief revenue officer told councillors the company would invest “in excess of £2 billion”.
Why it was deferred
Three things came up repeatedly in the debate.
Water. Ark expects the whole campus to use about 7,584,580 litres of water a year at full load, according to the update sheet. That is about 12 times less than the hotel used when it was open, Ark says. One councillor quoted notes of a meeting at which Affinity Water told the council its current plans do not account for data centres. Affinity’s response in the officers’ report raised no objection and dealt with protecting its nearby public supply boreholes, not with capacity. The committee asked for written confirmation of capacity before deciding.
Height and design. Several members said they had no objection to a data centre on the site, only to buildings of this height beside homes, the traveller site and the Bushey Jewish cemeteries.
What the developer pays. The planning obligations on the table include £91,500 for A41 crossing and highway works and £6,000 for travel plan monitoring. Officers told the meeting that the approved DC01UK data centre at South Mimms brought £571,100 in contributions plus a separate £5 million to the council. They also cited £12 million for skills and training paid on a Three Rivers data centre allowed on appeal. Councillors want officers to seek more.
The motion to defer “on all grounds” was carried. The chair then closed the meeting at 9.32pm.
What happens next
The application stays undecided. It will come back to a future planning committee once officers have the water response, a fresh look at height and design, and the outcome of talks with Ark. The council has not said which meeting. The next one is on Thursday 26 November, and its agenda is published about a week before.
The site already had outline permission for a warehouse scheme, granted in 2023, but that permission has now expired.
What it means for you
- If you live on Sandy Lane, in Patchetts Green or at the caravan park: nothing is decided, and the committee has asked for more on the points objectors raised. The reference to follow on Hertsmere’s planning portal is 25/1781/FUL.
- If you use the A41 between Watford and junction 5: the scheme includes a new signal-controlled crossing at Sandy Lane and a cut in the A41 speed limit to 50mph. None of that happens unless the plans are approved.
- If you want to watch: Hertsmere’s planning committees are broadcast live on the council’s YouTube channel and meet at the Civic Offices, Elstree Way, Borehamwood. For planning applications inside the town, see our Watford planning news page.
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