The thing that muddies the waters here for me is that UBS have a...

The thing that muddies the waters here for me is that UBS have a stake in Regal, so it's kind of confusing for me.
In a general PB relationship the PB will hold custody of the shares the corp client owns (but the client remains the beneficial owner). If the PB relationship allows then the PB can lend that stock out and the owner may receive a rebate for allowing them to lend.

Theoretically here I would say if Regal wanted the price capped they could allow the stock to be lent by the PB to shorters and they would get the benefit of rebates for allowing shorting as well as lowering the price to accumulate. Given that Regal is partly UBS then UBS gains as they are effectively the client and the lender, so they would get the short rebates, lower price to accumulate as well as fees paid from those borrowing to short (who will have to buy back eventually). So I'm guessing this is a win win win for UBS. All IMO of course...