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Anyway, this is what the tracks look like now, as of January this year. The track refurbishment programme - called 'Kings Cross Uncrossed' - involved opening up the third tunnel on the approach to the station, which hadn't been used since the 1970s. Among other things, this allowed them to lengthen platforms a little, so that longer trains could call at Platforms 9 and 10 ... and you may notice that there is no Platform 11 any more. Longer trains mean more passengers can fit into fewer platforms; so Platform 10 has been mothballed, and Platform 11 re-numbered to 10.
In short, as a result of this engineering work there's now an empty space between Platforms 9 and 10, where Platform 10 used to be ... sort of a Platform 9¾.