Wm Morrison was all set to be kicked out of the FTSE 100, but thanks to strong sales growth data from Kantar Worldwide, which helped the shares to firm on Tuesday, it looks as though it will be able to hold on to its spot in London's top-flight index.According to the Kantar data, Britain's fourth-largest supermarket operator, increased its quarterly sales for the first time since December 2013, outperforming its rivals.Wm Morrison's relegation to the FTSE 250 was due to be confirmed as part of the latest quarterly FTSE reshuffle, which is based on Tuesday's closing prices and will be announced after the close on Wednesday.According to calculations by Citigroup, support services company DCC is likely to be promoted from the FTSE 250 to the FTSE 100, while engineering firm Meggitt will be demoted to the 250.