It's obviously not perfectly safe, but is certainly complicated for the US to use UK business records in order to track down growers. And the DEA isn't going to devote any resources to catching somebody who is growing a few plants for themselves, they'll really want larger growers who distribute. A try to search for the number of convictions for growing versus posession and selling, there are very few. But keep in mind that the UK is our closest ally, and only make small orders.