Go like the clappers
Go very fast; in a vigorous manner.
This term isn't common outside of the United Kingdom, and is now considered rather archaic even there. It originated around the time of WWII as RAF slang. The earliest citation I can find is from a 1942 newspaper piece by Associated News staff Writer Alfred Wall, in which he listed various RAF slang terms:
"A pilot chased by the enemy 'goes like the clappers', or full out".
What 'the clappers' refers to isn't entirely clear, although by far the most likely derivation is as a reference to the clappers of bells. An early form of the phrase was 'go like the clappers of hell' and, given that bells have clappers, it may be that it may that the rhyme of hell and bell is significant. RAF pilots were often from English public schools where the ringing of handbells to mark the time was common. Bells were rung more vigorously as the time remaining to get to class/chapel etc. was about to run out. The image of schoolboys dashing to class while handbells were being energetically rung matches the meaning of the phrase very well.
There is another suggestion, that it was first rabbits that 'ran like the clappers'. This notion comes from the French word for a rabbit hole - clapier, which was adapted into English as clapper. Rabbit burrows, especially those that were constructed in order to breed semi-tame rabbits, (or conies, as they were then called) were called clappers. This was known in the 15th century; for example, from the romantic poem Roman de la Rose, 1405:
"Conies... That comen out of her claperes."
The proposal has two significant flaws. Firstly, the phrase and the meaning don't match. Rabbit would have 'run from the clappers', not 'run like the clappers'. Secondly, the 'rabbit-burrow' meaning has long been archaic and unused. The most recent example of its conversational use that I can find in print is from 1725, although there are still some place names that derived from this source - for example Sharpenhoe Clappers in the English Chilterns.. The phrase originated in the RAF in the mid 20th century - long after clapper meant something else entirely.