BA have enough aircraft. It’s just taking a while to get all the crews trained for Mainline, Euroflyer and indeed Cityflyer. After two years of the pandemic it will take a while to get everything up and running. Hence some short term wet leases may be possible. The main shortage is more cabin crew than pilots.
I am confident that the inaugurals for Euroflyer will use BA aircraft especially with all the press covering the event.
TUI, Jet 2 are also having to lease in planes to cope with demand and training issues.