Canon at Elstree can be helpful, but it's not the easiest place to get to if you don't have your own transport.
Not sure what the CPS membership from the US will get you here, you'll have to call them. If you're lucky they may be open tomorrow, otherwise you'll have to wait until Wednesday because of the New Year holiday here.
Canon's other main agent in South East England is Fixation http://www.fixationuk.com
They're easier to get to being in central London and a short walk from Vauxhall tube station, but they won't be open until Wednesday 2nd Jan. This is definitely THE place for Pro service in the south east, if you can't get a loan body via your CPS membership Fixation have a good rental business.
I think either location will do same day repairs, assuming any spares are available, they may also be helpful with respect to mailing a body back to you by next day delivery courier too. Our Royal Mail postal service have a "Special Delivery" service which guarantees next day delivery for valuables at a reasonable cost, most post offices can also sell you suitable packing too if getting to London isn't an option. I don't think there anything nearer to Chichester that can help.
My own preference would be Fixation, but you may be able to get a loan body from Canon if you're CPS which might swing it for you.
Fixation also might be a win for you if you want to visit London anyway. There's some good photo exhibitions on in town at the moment, eg the Taylor Wessing Portrait awards at the National Portrait Gallery, plus it's just a great place to visit even in the rain ;-)
Hope this helps