Sorry for double posting. I shared the post to twitter but since I had fiddled with settings in share2steem to make it post everything from Twitter automatically, it then proceeded to post the Tweet I'd shared from Steemit directly back to Steemit. Hence the double post.
Be careful if you use the 'share' button to share stuff to social media AND you also use share2steem!! .....or perhaps its just this old plonker and no one else would do such a silly thing ;-)