It looks like someone has changed the address, on the POI version, mis-spelling part of it, and using housename and number strangely, without actually changing the location to match the new address.  The correct address is Unit 3, The Hawthorne Centre, Elmgrove Road, and is at the railway end of Elmgrove Road.

The Hawthorne Centre is multiple buildings.  It is a gated, and I was looking towards the end of working hours, so wasn't sure if the gates  were about to get locked, so didn't go in.   However, I think that unit 3 is part of https://www.openstreetmap.org/way/924569806.  Probably just the half nearest Elmgrove Road.

The sign at the entrance to the estate lists it as "Royal Mail Harrow".