On your confirm.php page lines 89-93 you have:
$WA_PP_ECO_Set_params[0][$nextIndex] = "ReturnURL";
$WA_PP_ECO_Set_params[1][$nextIndex] = "http://localhost/pp_confirm.php";
$nextIndex = count($WA_PP_ECO_Set_params[0]);
$WA_PP_ECO_Set_params[0][$nextIndex] = "CancelURL";
$WA_PP_ECO_Set_params[1][$nextIndex] = "http://localhost/cart.php?ppcancel=1";
It looks like you have it set up to use your localhost. That has to be updated to use your live site like:
$WA_PP_ECO_Set_params[0][$nextIndex] = "ReturnURL";
$WA_PP_ECO_Set_params[1][$nextIndex] = "http://www.usedmagic.co.uk/pp_confirm.php";
$nextIndex = count($WA_PP_ECO_Set_params[0]);
$WA_PP_ECO_Set_params[0][$nextIndex] = "CancelURL";
$WA_PP_ECO_Set_params[1][$nextIndex] = "http://www.usedmagic.co.uk/cart.php?ppcancel=1";