If Belgium isn't attacked and the British start off neutral, yet want to support their friends, what scope is there for "acts short of war"? I'm thinking of things like:
[1] Declaring a trade embargo on Germany
[2] Declaring the Channel and southern North Sea to be a total exclusion zone (presumably they'd escort some convoys through to France, Belgium and the Netherlands
[3] Just declaring a blockade and telling anyone who complains to either shut up (Central Powers) or that Britain/France will buy their trade goods instead (the US)
[4] Making a deal with Belgium to send troops in to "guarantee her independence", which would produce a direct threat to northern Germany (I think this is a non-starter for that very reason but it might work if it were expressly limited to the Channel ports)
The naval ones are essentially acts of war against Germany, but the whole point here is that Germany needs to avoid war with Britain and therefore can't retaliate.
I think [2] and [3] (at least if it is a blockade of naval vessels) are almost guaranteed. I think most commenters here seem to think so, too.
An embargo is more of a "Phase 2" response - though it is possible that Asquith might find some way to restrict shipments of critical materials or goods to Germany or Austria "de facto."
Sending in troops would be a harder sell in London once the decision has been made to stay neutral - and it would, in any event, require Belgian approval.