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Google Analytics calculates bounce rates as a percentage of people who enter on a page and fire the sendPageView event but never A) send a second event by going to a second page within the same domain or B) Interact with the page to either provide another page view or conversion.
I am not familiar with Clicky and how it tracks its page views so I can't really help on that front.
It gets tricky to do it right but essentially you have to set your primary domain and than create a filter for the sub-domains. The link below breaks it down for you in depth.
https://developers.google.com/analytics/devguides/collection/gajs/gaTrackingSite
Building on Patrick's answer using Robots.txt was the fastest way for things to take effect, but if implemented wrong can impact you pretty bad.
In addition to adding the exclusions in the Robots.txt, I also put in a removal request to remove the pages with parameters from googles index using the Google Url Removal tool, this combined with the other options helped clean up my results in the google index.
Hope this helps.
As of this writing it looks like the page is indexed. By searching site:ukjuicers.com it comes up in the search results with about 861 other results. Not sure if there is anything you changed to get things working again but it seems to be in their index now.
Try running Google tag assistant chrome extension it shows you the tags that are currently showing on the page you are viewing. I say this because it might be a second pageview event that is firing when someone goes to one of your pages. That can cause your bounce rate to drop because it tracks two pageviews for every one page they visit, unless they leave the page before the second event fires.
Are the bounce rates for these pages the ones that are lower than expected? If so that might be the case. Use the chrome extension to help you diagnose the problem it will tell you what is being fired. You can see if it is firing 2 page views or just the single page view which is normal.
Did you take a look at the help page? You might need to have your developer or whomever setup your Google tag manager account to take a look at the code on your site as well as your tags that are setup in tag manager.
https://support.google.com/tagassistant/answer/3207128?hl=en&ref_topic=2947092#nonstandard