"Having to wait" not as in actually waiting (e.g. as if Brussels would somehow slow down the pace of law-making in the UK) but in the sense UK will have to be handed down to adopt and enforce EU laws. So, wanting to make a law about X, in the sense that UK citizens see it and to their interests? Tough luck, unless it matches the EU law on the subject.
So the answer to your question is, in any and all cases where the UK law doesn't agree with EU laws.
EU laws goes above national laws. This is based on "The primacy of EU law" doctrine.
https://en.wikipedia.org/wiki/Primacy_of_European_Union_law#...
Here's one particular example upon many:
The latest battle is over Brussels’ impending ban on the weedkiller glyphosate, the U.K.’s most widely used pesticide, largely due to political pressure from green groups on the Continent already skeptical of pesticides and certain other new technologies in agriculture. But pulling glyphosate, better known as Roundup, from the market, would be devastating to British farmers who rely on the herbicide to treat weeds.
http://www.politico.eu/article/glyphosate-weedkiller-decisio...
You really did not know that there has been frequent tension between national laws (in the UK and elsewhere) and EU laws in all kinds of aspects (from labor laws to agriculture and shipping), or were you trolling?
(If not from EU or UK I can understand it, because you wouldn't be familiar with the subject matter -- but it's a very common occurence, and a very common theme in the news in EU countries).