I haven't seen this posted anywhere yet so just thought I would write this up so it might help others. I just found a setting that finally allows you to change the general default currency in vCAC. As far as I am aware it is only available in 6.1.
Go to Infrastructure > Administration > Global Properties and edit the "Configured Currency Region Name". For UK £ I changed the Value field to en-GB and restarted the vCAC appliance and the IaaS servers.
Danny