Converting my Opencart multi currency checkout basket to convert to single currency for Barclaycard ePDQ payment gateway

Basically, my website has the option for three currency Euro, pounds sterling, and us dollars, but if a customer has items in the basket that are in euro or us dollar then when they click the ePDQ Barclaycard payment link radio button, it then goes to the Barclaycard ePDQ (BUT THIS ONLY ACCEPTS POUNDS STERLING), so the payment wont be process. So I need a Opencart script/ module that will convert the currencies to UK pounds (depending on the rate that day) so that when it hits the ePDQ platform it is in the UK pounds currency, and then the Barclaycard ePDQ. Need experience of Opencart version 1.5, Barclaycard ePDQ integration,