So, this falls into the same trap that an awful lot of theories about why <insert country> fought WW1 in that it tries to ascribe a single overarching motivation to what was, on all sides, a deeply complex set of motivations. Now, I'll freely admit to preferring certain interpretations of WW1 in accordance with that view, but I don't think it's particularly controversial to note that there's really no single cause for the war and no single reason for any of the countries that fought in it. Additionally, we should be careful to distinguish between direct and proximate causes of the war. I.e, the clash of interests between Great Powers and the formaton of the alliance systems enabled the war but the assassination of Franz Ferdinand and the escalating crisis actually caused it.
So, in this case I think it's fair to say that pre-existing economic and political rivalry between Britain and Germany was a cause of British entry, but it goes much too far to say that the British government entered the war to crush an economic rival. It's similar to the discussion that arises when someone asks if Britain really entered the war because of German aggression against Belgium. The answer can be both yes and no depending on what you consider to be a cause. In this case I would contend that the actual reason Britain went to war against Germany was to prevent the defeat of France and secondarily to preserve a vital continental ally and to ensure that war with Germany happened in the best available circumstances. But the reason those things mattered was the underlying Anglo-German rivalry.
I hope my point about the distinction I'm trying to make is clear, even if it isn't especially well organised. But that's enough rambling from me for now.