Thanks. That'll have been it: I was using my spread-bet account and later foudn I could short other, presumably more liquid stocks, so it's was a matter of no borrow.
Thank you for clarifying.
JFB3
My understanding is, if it isn't a guaranteed stop loss, your position will become a market sell order at opening if the bid price is below 1511.
That's 'weekend risk' and why many swing traders close out on Friday.