UK shares: Easyjet and Ithaca join FTSE 100 in quarterly reshuffle; Persimmon and Entain drop down

• Easyjet and Ithaca Energy to join the FTSE 100 Index, with Entain and Persimmon to leave the Index

• Five changes to the FTSE 250 Index

FTSE Russell confirmed that Easyjet and Ithaca Energy will join the FTSE 100 Index as a result of the September 2026 quarterly review. In the rebalance, Entain and Persimmon are being demoted from the FTSE 100 Index and will enter the FTSE 250 Index.

Easyjet joins just before it’s due to be taken private after the airline agreed to a £5.7bn takeover by Apollo, following a protracted bidding war by US private equity groups. The takeover approach has sent shares up +31% YTD – a bittersweet re-entry into the index for the airline. It’s due to complete the Apollo deal in the first quarter of next year. 

Ithaca Energy shares have risen 68% this year on hopes it will soon gain final regulatory approval to develop the Cambo project. The oil and gas company also has a 20% stake in the Rosebank oil and gas field, which is currently subject to a decision by the government on whether to approve new drilling licences. Whilst the previous Labour government under Keir Starmer halted new licences for drilling in the North Sea, there are signs that Andy Burnham is keen to let some go ahead. A 9.5% dividend yield has supported shares alongside improved guidance but regulatory overhang is a consideration.

Of the two stocks leaving the FTSE 100, Entain has been hit by a lack of progress at its US BetMGM business in the US, while Persimmon has seen its shares slide as part of a broader pullback in the UK housebuilder sector as higher interest rates and rising input cost inflation and labour costs hurt building activity and margins. It’s hard to imagine much more clarity for the sector before the Autumn Budget on 28 October.

Moving up to the FTSE 250 are Pinewood Technologies Group, an automotive software developer, and Volex, which makes power and data transmission products. Volex shares jumped last week after it reported strong profit growth and raised its outlook.

Another joining the mid-cap index is Seraphim Space Investment Trust, which is a newly listed multiple line of existing constituent, Seraphim Space Investment Trust. I had a look at this earlier this year.

Relegated from the index are GB Group and Aston Martin Lagonda Global Holdings. 

All changes from this review will be implemented at the close of business on Friday, 18 September 2026 and take effect from the start of trading on Monday, 21 September 2026.