Coolant pump belt change

My 1.8tsi Octavia scout coolant pump was leaking via the impeller. I'd like to change the small belt (not the big timing belt!) that spins the impeller as well as the pump etc but the left handed bolt is stuck. I've not tried too much force as the captive gear it holds moves when I try and I'm concerned that I might break something internally. Would anybody have any experience removing this bolt or known methods of doing so?

The photo shows the gear and the bolt I'm refering to is holding this gear and is just out of sight.

Thanks

Edited 5 hours ago5 hr by Flyinghigh