Are wheel clamps effective

Yes!  Wheel clamps come in a wide range of styles and choices, and for various sized vehicles. The visual deterrent of a wheel clamp is often enough to deter a would-be thief into moving past your clamped car, or towed vehicle, and on to the next. 

In most cases, wheel clamps are generally a lower cost than the insurance policy excess would be should you have to claim for a stolen vehicle.