Re. tipping cash v buying a drink (UK)

I have played pubs as a semi-professional where people who worked under me in my day job were present.
They would come to talk in the interval & offer to buy a drink 'cos they liked a particular song or request.
I would accept thankfully.
Whereas if they offered money, I would be embarrassed by the fact that both me and they knew that I was earning more than them in our day jobs.
I have played in restaurants where patrons bought me 'drinks' & the barman put the cash aside for me.
I have also performed floor-spots when a few listeners have said they enjoyed me more than the guest. Who should they tip?