Companies explicitly specified by direct selection.

This list was extracted on the 4th of Febuary 2020, from:

The FTSE 250 Index (/ˈfʊtsiː/ FUUT-see) is a capitalisation-weighted index consisting of the 101st to the 350th largest companies listed on the London Stock Exchange. Promotions and demotions to and from the index occur quarterly in March, June, September, and December. The Index is calculated in real-time and published every minute.

Related indices are the FTSE 100 Index (which lists the largest 100 companies), the FTSE 350 Index (which combines the FTSE 100 and 250), the FTSE SmallCap Index and the FTSE All-Share Index (an aggregation of the FTSE 100 Index, the FTSE 250 Index and the FTSE SmallCap Index).

Many companies within the index are investment trusts. As of 30 September 2008, the net market capitalisation of the FTSE 250 Index was £161 billion (or 13 per cent of the FTSE 100 Index).

Source: Wikipedia