Hi,
I'm currently doing a joint in Econ and Maths at Stirling.
I know a couple of people doing PPE who haven't done higher maths - they find the maths involved in Economics quite challenging. This is mainly an issue in intermediate and advanced micro and advanced macro.
However, as all other degrees, only your grades in 3rd and 4th year count towards your final classification.
It's only up to 5th semester (1st semester in 3rd year) that your cores modules are chosen for you in Econ on PPE, so after this you are free to chose any economics courses you like. So most PPE students I know are currently doing the economics modules with less maths i.e. environmental economics, behavioural economics etc. and really enjoying it!
So it might be a struggle through intermediate and advanced micro, but after that you are free to chose for yourself.