Following the recent refusal of the controversial HMO conversion at 149 Herlwyn Avenue on 20th March, a new planning application has already been submitted for the site.
While the previous application for a six-person House in Multiple Occupation was rejected due to over-intensification and poor living standards, this new submission represents a notable change in strategy.
LATEST UPDATE:
Enforcement and Owner’s Statement
Following the Council’s refusal, the Hillingdon Planning Enforcement Team has been in direct contact with the owner. The owner has now formally stated that they will not be pursuing the HMO conversion and that the property will remain in use as a single dwellinghouse.
The Enforcement Team continues to monitor the site, as building works are currently proceeding at the owner’s own risk while the new application is being determined. Following Ruislip Residents’ Association’s enquiry, the Council is also seeking clarification on why the latest application was not explicitly labeled as “retrospective“.
How the Proposals Compare
The most striking difference between the two applications is that the new “Householder” proposal actually seeks to create a larger building footprint than the refused HMO plan. Despite moving away from a high-occupancy use, the physical scale of the development has increased.
| Feature | Refused HMO Proposal (Dec 2025) |
Householder Proposal (March 2026) |
| Application Type | Full Planning Permission | Householder Planning Permission |
| Proposed Use | 6-bedroom, 6-person HMO (Use Class C4) |
Single-family dwelling (Use Class C3) |
| Internal Area Gained | 48.40 sq. metres | 50.60 sq. metres |
| Scope of Works | Rear extension | Rear extension plus loft conversion with dormer |
| Additional Rooms | Conversion of existing layout | 1 new bedroom and 1 new bathroom |
| Application | 19188/APP/2025/3239 | 19188/APP/2026/820 |
Why the Increase in Size?
The increase of 2.2 square metres in the new application is primarily due to the inclusion of a loft conversion and rear dormer, which was not part of the original HMO floor area calculations. While the HMO plan focused on squeezing maximum occupancy into the existing and extended ground floor, the new plan utilizes the roof space for a single-family setup.
Ongoing “Retrospective” Issues
Residents should note that the “part-retrospective” nature of this development continues. The new filing explicitly states that building works commenced on 1st January, without prior consent. The applicant now expects the current phase of construction to be completed by June 2026.
In Perspective
Because this is now a Householder Application, the applicant has claimed an exemption from Biodiversity Net Gain (BNG) rules.
While a householder extension is generally less intensive than an HMO, we are concerned that the increased physical scale (now over 50 square metres of new space) must still respect the character of the road. We will be monitoring to ensure this is not a “backdoor” attempt to facilitate the previously refused over-intensification under a different name.
Next Steps
We encourage residents to view the new plans on the Hillingdon Planning Portal under reference 19188/APP/2026/820. We will continue to watch the application as the consultation period for this new application begins.
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