In my opinion the UK is not much use as a partner for anyone in such a venture. When the Concorde project was originated there were numerous companies in the UK doing leading edge aerospace work, now the industry is completely run down.
After the Rafale/Eurofighter situation, there are no suprises in the Franco/Japanese collaboration. It will be the first and last between these two nations.
The real suprise will be if anything ever comes of it.