I too am in Leathermarket Court. Gross Fine seem to be the people who put up the notices in February of this year that they would be resuming clamping in the parking lot (evidence of which I have yet to see), so I assume that they are the managers. They do not, of course, include their telephone number or other contact details. They have a website - www.grossfine.com
If I recall correctly, however, having done a Land Registry search on the complex a while back, a totally different company is registered as owning the property.