From your description, it sounds like the hole in the lowering block where the spring's centerbolt fits in, is too small, & the licenced motor vehicle repairer that you paid good money to, in order for them to perform a professional job, has just bolted it together anyway.

If this is true, then they have retrurned the car to you in an unsafe condition & are probably guilty of an offense under the act.

The top & bottom faces of the lowering block must be firmly sandwiched between the spring leaf & the mounting pad on the axle housing with no gaps whatsoever. It sounds like the 'qualified tradesman' isn't so qualified after all. I wonder if he has a licence? If not, then that would also be another offense.