It is phrased that way to reduce the VAT element of the bill compared to if the word "discretionary" had been left out. For those that do not object to the service charge then the restaurant has saved the customer a higher vat (tax) bill which would otherwise include vat tax on service as well as the meal compared to if it was automatically added as "non-discretionary" as in many other cities and countries.

By all means have it taken off and don't tip. But if it isn't a problem and if the tip were say £5 then the word "discretionary" has actually saved you £1 tax which wouldn't benefit you or directly the people that served you - it would simply make the bill £1 more - and would instead help "the rest of us" reduce the terrible deficit we now have as a result of .... well I won't blame people on the "Upper East Side" because I think we're all innocent casualties - but you get the drift.

Hopefully, now that you have had it explained you will say how great it is that even under the terrible circumstance we find ourselves in that our cunning spunky British service industry has found a way to reduce the tax for our very welcome overseas visitors.

If you don't like it ... shrug and have it taken off .... but it was there to save most people tax .....