Congrats Nick. Unfortunately there are not many studies out there for the UK on salaries. We have recently completed a crowd sourced salary study with CMX. This post focuses on North America, since 95% of all answers were in this region. You will see bonuses are a big part of competitive compensation in North America for CMGR's. http://cmxhub.com/cmgr-salary/
I have some data points for the UK too, but not in a blog or graph format for now. So here it is:
Personally I have been incentivized with bonuses for the last 5 years in my CMGR roles in North America. It has always been tied to two things: 1) overall company performance (determines the % funding of my total bonus achievable per quarter) 2) % achieved of my quarterly expectation (tasks, campaigns, projects).
If you want an example of what a quarterly MBO structure looked like, I am sure I could dig one up as an example.
Ultimately the calculation looked something like this (Fictitious numbers):
Company overall performance hit 80%
Personal MBO completed 90%
Quarterly Bonus = (Personal Incentive $ x Company Performance %) x Personal MBO completed
$1,800 = ($2,500 x 0.8) x 0.9