I've just pulled into Witham on the 10.48 ex Liverpool Street service to Braintree on platform 4, and on platform 1 there are a pair of 317/6's, one of them being 652. Why are they here? I know the 17.02 to Norwich is planned to be 317 operated as are the Harwich services from London, but I didn't realise they had any booked work up the GEML now. Or is this a one off, and if so, what are they doing here? Many Thanks. 
