We have not really ever dealt with trade policies so i am afraid i dont really know the ins and outs of them.
We do run schemes that are designed for people with 2cars so can normally get pretty good deals in this situation (particularly if one car is pre 1992 as it may qualify for classic!).
If the claim was reported to your insurer then always declare it. If it is non fault and nothing paid out it should have no effect on the premium anyway so you have nothing to lose and have covered your own back then.
Hope that helps
Martin