If Britain remained neutral, I doubt very much that it would have anything to fear from Germany, at least militarily.
Prior to the defeat of Russia that is correct. After the defeat of Russia, Germany's options would open up and Britain's would narrow, and Britain would have a great deal indeed to fear from Germany.
This goes back to fundamental Germany strategy - which was to isolate and defeat individual members of the Entente before moving on to the next one. British neutrality on the basis of Belgium would play into that strategy by isolating Russia so that Germany could then defeat her.
Until Britain entered the war against Germany, I'm unaware that any serious German belligerent intentions existed towards her.
If Britain is neutral than Germany shall defeat Russia - maybe in 1916, or perhaps Russia switches sides (allies with Germany after denouncing its alliance with France).
After Russia drops out of the war, either France asks for terms from Germany (and we understand that these terms are not going to be as lenient as Germany would have granted in 1914), or France fights on.
If France surrenders, then Britain is in danger of seeing France going over to Germany after the war, (because no viable alternative policy alternative exists). If France does not surrender, then Germany and Austria will come at France straight through Belgium.