It’s the end of a meal out and you’ve been presented with the bill. Suddenly the pleasure of the food you’ve just eaten is replaced by a faint wave of anxiety as you realise you’ve got to work out how much to tip.

If you tip too little will you face the wrath of the waiting staff? Will you end up tipping too much? And if the service was bad, should you tip at all?

The debate is not restricted to restaurants – gratuities can be offered to many workers including hairdressers, taxi drivers and hotel porters.

A new law means workers must receive all of their tips – which is expected to benefit some three million workers in England, Scotland and Wales.

But there are no hard and fast rules about how much you have to leave.

Mae, a 17-year-old waitress for a small business, says she doesn’t expect customers to tip on top of the service charge that is added to the bill.

“So it’s quite unusual for customers to tip afterwards, which is fine. Lots of customers actually double check that when they’re paying that there is service on there and that it gets divided fairly.”

But she says one of her friends works somewhere where they don’t add a service charge so the customers there do tip – mostly.

A tip is “an uncalled for and spontaneous payment offered by a customer,” according to the government, whereas a service charge is “an amount added to the customer’s bill before it is presented”.

Etiquette expert Laura Akano, from Polished Manners, says it’s always “up to the individual” how much to tip but thinks “it’s important to show appreciation if you’ve had a good service”.

If a service charge is discretionary you can ask for it to be removed. If it’s mandatory you can’t – but the establishment must make this clear to you verbally or in writing before you order.

Both tips and service charges may be shared between many staff – for example, the person who brought you your dish as well as the one who washed it up.

Peter, 40, from Leeds, says the most memorable tip he got was from his two favourite regulars in a pub.

He knew them well, and would have their pints poured for them before they reached the bar.

One evening he was closing up and they invited him to join them – at a local strip club.

“They paid for all my drinks, and a dance for me,” he says. “That was generous.”

On his final shift at the bar some other regular customers pressed £10 notes into his hands and wished him well, “which was very kind of them”, he says.

However, he has also worked in restaurants where tips were withheld by the management, and a hotel where the service charge was never paid to staff.

“But when you need a job, and that’s what’s available, you don’t really argue too loudly,” he says.

The new law means the service charge must now be paid to staff.

It’s entirely up to you how much you leave as a tip, but many tourism websites suggest leaving about 10% to 15% in the UK.

Where Mae works, a 12.5% service charge is added to the bill.

Jemma Swallow, who used to own a tea shop in London, says 10% “covers most situations, without leaving the customer resentful of being asked for it and the staff for not receiving one”.

Ms Akano agrees that 10% is about right. “Whether people do that or not is a different thing but it’s nice to have a guide.”

Outside the UK, in countries such as the US, tipping can involve paying more than 20%, which is often compulsory even if the service is mediocre.

Mae says she doesn’t tip in the UK because the service is almost always included, but did when she went to the US.

“I did tip every time because the tipping culture is different there. That being said, it was a bit uncomfortable at times.”

In some Asian countries tipping is seen as rude, although the spread of Western-brand hotels is making the practice less of a taboo.

“Penelope”, not her real name, is a kitchen manager and says the level of tip depends on where you’re eating.

If it’s a Hungry Horse, you have certain expectations of what the meal will be like, and will tip accordingly. If you’re dining at the Ivy, however, you’re likely to tip more “to give the impression you’re a big spender”, she says.

“At the end of the day, it’s theatre,” she adds.

If a discretionary service charge has been added to your bill and you don’t think it should have been then you have the right to ask for it to be removed.

Regular restaurant goer Nige Eaton, 56, from Bedfordshire, says he’s always been concerned that tips don’t reach staff, and doesn’t like eateries that automatically add a service charge.

“When it’s printed on the bill, it does feel like some sort of blackmail and some customers feel forced to pay it, which is wrong,” he says.

If staff do a good job, they should be tipped – but this should be down to the customer, he says.

Etiquette expert John-Paul Stuthridge says it’s prudent to check restaurant websites to see whether a service charge is included “given the prevalence of ‘surprise’ service charges”.

“You could ask a member of staff, but discretion is the name of the game, so try to ask them swiftly and out of earshot from your guests.”

Ms Akano suggests letting a member of staff know you’re unhappy about the charge before the bill even arrives. This way they might remove the service charge for you.

Tipping in many industries has evolved from the days of leaving spare change on a table, with card and contactless payments now the norm.

However, “the spirit of tipping to thank hardworking staff remains strong,” says Kate Nicholls, chief executive of trade group UK Hospitality.

“If you want to tip a particular person, a cash tip will allow them to keep it themselves, while leaving a tip on the bill or behind on the table will benefit the whole team, from front-of-house to chefs and kitchen porters working hard in the kitchen.”

An alternative to tipping in the 21st Century could be leaving a social media post, which people increasingly do, and is “honestly very appreciated”, according to Mae, who says her bosses “are really on it with things like reposting stories where people have photos of the food”.

Mr Stuthridge says leaving a positive review on social media can actually be worth more than a good tip, depending on the size and nature of the restaurant.

“The time and energy spent to leave a good review probably helps the business more in the long term than any loose change could.”