this is very unrealistic britian wont sell them free of charge and yet open its source code to be manipulated. if anything britian has its partners and itself to upgrade these aircraft but it is deemed costly and complicated as u said. lets say you get these aircraft you wont get the meteor as france will reject selling it due to political tensionsThe UK has around 30 'active' Tranche 1s which their useful airframe life have not yet been halved. Around 15 aircraft are also kept as spare parts. These planes would initially go out of service in 2019. Then it was delayed to 2025. And if I'm not mistaken, I've read a few other articles about the extension to around 2030. These planes have been a headache for the Royal air force in recent years. At first it was announced that these planes could not be upgraded to T2/T3, but later it turned out that this was not true, but still the problem was quite complex. Maintenance logistics, software problems and some specific design limits are known to exist.
If Britain wants to get rid of these planes it can give it to Turkey free of charge (by opening the mission computer and some other avionics to the Turks). As a result, these aircraft will be logistically dependent on the British aviation industry for at least another 15 years. Of course, in addition to the transfer of ready T1s, a purchase agreement can be made for example 2 fleet tranche4s.
This is hypothetical, but cant say it is improbable. Because most of the companies in the MMU project could be among the suppliers of the Team Tempest project. Likewise, the contribution of British and Italian companies to the MMU project is obvious.