It's a known that the current highest level from US-LHR is 320K one-way as it has a CSY3200 fare basis code. Since it's a 'Y' class award (the third letter in the basis code), there aren't any higher levels. The only way you could potentially produce something higher is through a broken-fare construction. So this is sounding like an upgrade based on cash price difference or FCM price at 1CPM.