Thanks guys. The chain setup will no doubt be more durable than that plastic clickbox. The little cover keeps dropping off. May be a possible mod.
I've found the gearing too low and have replaced the cassette and the RD to a road 105. Works OK but I suspect the chain needs to be narrower as it seems to snag and jumps two gears at the same spot. This change seems to have freed up bit more room for the fold. Once I have the replacement tyre on, I shall try and see if further fiddling is required. I may just add that Pacific chain tensioner for a neater fold.