Get cart_total in default store currency with local currency enabled

[DanWG]

We have an app that deals with our Finance payments, it only works when in our default payment (GBP) and is only available to those in the UK however, if someone is abroad on say a holiday/vacation the 'local currencies' feature kicks in and changes the currency from GBP. We don't want to disable local currencies as it is beneficial for our customers but as far as I can see the properties of the cart object are all converted.

Is there a way to get the cart_total or similar property to return in the store default currency (GBP) rather than the local currency? (this would be used for a hidden value for the app to use)

Thanks