Cast off, number one

My clients are a mother (M) and father (F) who own 50% of a trading company; number one son (X) owns 35% and number two son (Y) owns 15%.

X wishes to leave the company and the parents have the money to purchase his shareholding.

They also wish to give Y more shares in the business.

The trading company has been owned for more than two years so all shareholders currently qualify for 100% business property relief (BPR) on their shareholdings.

However if parents M and F purchase X’s shares and then make a transfer to Y does that transfer still qualify for business property relief?

My question is how does one identify which shares have been transferred to Y?

Are they the newly purchased shares or are they the parents’ original shares?

I should be grateful for any clarification or advice that readers might be able...