Just to update and close this off. I called back again today, they offered me a reroute via PHL, but it got in to LHR too early to be convenient for me. The fella I spoke to seemed more than happy to change my flight to one leaving BOS a couple of hours earlier though.
It did take 35 mins on the phone to conclude though! Not a problem for me, I just worked with a headset on, horrific for them though if it was actual time it was taking this guy and the person he was supposedly communicating with to fix!
Thanks again all who advised to HUCA