Having now looked through several manufacturers/suppliers websites, it is widely and commonly confirmed that the shorter, improved pre-facelift Accord i-CTDi belt needs to be 1785mm... this then gives a Gates/'universal' part code of 7PK1785. However there is a good deal of confusion regarding this code, as the Gates website wrongly suggests that this is only for various Renault models, and only lists the longer, obsolete Honda belt. Many suppliers then regurgitate this incomplete information! So Woody - if you're reading this - you were bang on with your advice and I apologise for having doubts (it was the exclusively Renault advice from Gates that worried me).
I have just ordered a belt from CarParts4Less (via eBay) for £12.60, delivery included.
For info (and to help avoid buying the wrong part) the longer, obsolete belt length is 2265mm. That belt size is still widely available.