Some might say that, since obtaining a CSCS card is not mandated by law, you can get a construction job without it. And to a certain extent, they're right. However, all reputable construction companies today require workers to have a CSCS card, and frankly, every government from the village level to the national level that needs roadwork performed is going to insist all works have proper training and certification, So if you're satisfied working on the edges, likely for a lower wage and with little chance of advancement then by all means don't get a CSCS card.
About the CITB HS&E Test
In total, there are more than a dozen different CSCS cards intended for workers with different responsibilities. But every one of those different workers must pass the CITB Health Safety & Environment (HS&E) test because it covers principles of safety and health relevant to everyone.