Service charge: how do I know if the restaurant staff got my tip?

I was told my tip would not go to the restaurant staff. If I’d known I would have paid it in cashIn January I took my family to the German Gymnasium restaurant at King’s Cross, London. The food was good and the service excellent. The bill came to £336.43 including a discretionary 12.5% service charge, which I paid happily. But when I asked a waiter how it was shared, I was told none of it reached the staff, which I found disappointing. I have tried to make contact (by email) wi