Whilst it is OK to claim back the cost of a meal it is not always the case that an individual is able to claim back the tip via expenses unless there is a mandatory service charge.

I'm sorry for anyone who is forced to make their living from an occupation which pays below par wages and is forced to give 200% just to get a decent wage, but it does get out of hand. I recall a debate a few years back (on another forum) that centred around tipping of porters at US airports - the consensus of what was reasonable was such that I calculated that for a 40 hour week a porter working at an average rate could expect to earn over $150,000 dollars a year, in tips.

And about helping people out on performance related pay? Where will it end - Do I tip the salesperson of my car or furniture when I haggle the price down, knowing that the fact they have reduced the price for me may impact on their commission?

In the real world, I'd like to think that there are relatively few people who knock the tip down for relatively minor mistakes - but if things really do go wrong, and if it particularly is the fault of the wait staff you will NEVER convince me that I should pay the tip nomatter what. Even in places with a fixed service charge (and it has only happened once in 40+ years) I would be calling the GM over and negotiating the overall price I paid.