Right iv fitted a new chain and need the link riveting on, the bike shop says if I can pop it on temporarily and take it up there they'll flare the rivets.... Any ideas?

Use a split link, put on right it will be fine until you get to your shop. You will get varying views on split links as some people reckon they should be ok on a 400 if fitted correctly to use all the time. I prefer to use them as a temporary measure such as yours. Remember the round end of the split link clip goes to the front following the direction of travel.

Dave

buy a chain riveting tool and flair the rivets yourself.....

and never have to worry about the job ever again as you have your own tools.