BQ have spent time making you a good trainee now there could be several reasons why you were a better trainee than the others.
You have a natural talent for slab paving
You physically matured quicker than the other trainees which allowed for larger slabs being used and speed at which they were laid.
Now Homebase have let you know that they are willing to take a risk on you becoming a very good senior slab paver , they can afford it and if you don't make the grade, like the aforementioned Jordan Slew, they can take the hit.
You now go into BQ management and tell them the above scenario, while BQ possibly want to match Homebase they simply cannot take the risk as there have been plenty of YTS's up and down the country for multiple DIY stores that simply never got anywhere near their supposed potential.
So either you take a hit and BQ win.
Or you can win, homebase can win and BQ get shafted.
BQ could be pretty annoyed if it's the latter, all that training that has gone on before wasted, although they might get some Homebase vouchers.