It was the ultra-exclusive spa that first launched the words 'health farm' and 'wellness' into public consciousness in the 1920s when it was set up by an eccentric health fanatic.

Princess Diana was later a fan and guest at Champneys in Tring and stars including Kylie Minogue, Brad Pitt and Daniel Craig have all stayed there.

But now the country's first spa, which is more used to setting trends, is responding to a new craze it certainly does not want to lead the way in – as an increasing number of guests are said to be doing a 'dine and dash'.

And staff say more and more visitors enjoying luxury treatments at the spa, which typically cost £100 or more, are also walking brazenly off without paying.

Traditionally the £345 a night resort is 'cashless', not least because when guests check in they are given a white towelling dressing gown and flipflops to change into and are encouraged not to use mobile phones in public areas.

For years, the system has operated on trust where guests simply give their room number to staff when they have had a meal or a beauty treatment or ask for a bill if they are visiting for the day.

But an insider at the Hertfordshire resort which celebrated its centenary last year says an increasing number of guests who dine and drink in the hotel's gourmet restaurant are leaving without paying.

The situation has become so problematic staff have now been briefed to take payment at the table before guests leave.

A source told The Mail on Sunday: 'More and more people are sitting down and eating and drinking and then just walking off. Traditionally as we have some guests whose food is included in their stay and some whose isn't or some who are just there for the day, we rely on people's honesty.

'Now we have a lot of people who just walk off. It's become such a problem that all the waiting staff have been briefed to ask for payment for dinner at the end of the meal which can be embarrassing. I have read about the shoplifting epidemic, but I didn't think anything like that would happen here.'

One couple dining last week and ordering a bottle of champagne were astonished to find that they were asked to 'pay as they went along' for their drinks.

A guest told The Mail on Sunday: 'I am a regular here. Last night, I was asked to settle up for the wine I had at dinner rather than put it on to my room number. That has never happened before and I was really taken aback. I didn't have any money on me so they just had to trust me.

'And then I saw guests ordering champagne who were asked to pay for it there and then. They seemed pretty surprised but accepted it, but I was astonished as I've never seen that here before – in fact I have never seen anyone in a restaurant being asked to pay for drinks as they go along!

'It seems like the problem of 'dine and dash' has even spread to Champneys.'

Meanwhile guests having luxury spa treatments at the venue are also being asked to pay up straight away and are no longer allowed to charge it to their rooms.

One beauty therapist admitted they had all been told to ask guests to pay as soon as they had finished their treatments because 'so many people just nip off as soon as they can or even give the wrong room number' to avoid paying.

A Champneys spokesperson said: 'As with many businesses across the hospitality and retail sectors, we occasionally experience isolated incidents of non-payment or theft, though these remain rare and very much the exception rather than the norm.

'Naturally, we have sensible operational measures in place to minimise any loss to the business. 

'However, these are always handled discreetly and thoughtfully, ensuring they remain aligned with the premium, customer-focused experience Champneys is known for.'