When First Great Western decided to utilise dead space near a redundant exit at Oxford station, they probably were not thinking of the phrase: "When one door closes, another one opens."

But that is exactly what happened when the space was offered to South African couple Stuart and Kathy Hallworth, as it has allowed them to set up a brand new venture, a juice bar called Vitaburst.

With a turnover of £155,000 in the first year, Vitaburst has done so well that the Hallworths are about to expand to Reading station and then Bristol. So what is the secret of their success?

It must have something to do with the names of their juices and smoothies. Who could resist Flu Fighter, Instant Energizer, Power Surge and Forever Young? Yet Mr Hallworth insists the names are not a marketing ploy.

He said: "The benefits are there, so we're telling the truth. What we are selling is the outcome of what the drinks should do for you."

Having slurped through a few of their juices and smoothies, I would suggest the real reason they are doing so well is because their drinks taste so good, and help you effortlessly consume your recommended daily intake of fruit and veg.

"So many people have come and said: I really do feel better,' after drinking them for a few weeks," Mrs Hallworth said.

This is not surprising when you consider what is packed into the drinks. A Veg Out, for example, contains beetroot, celery, apple, carrot and ginger, while the Green Freak smoothie contains yoghurt, mango, pineapple, banana, orange and spirulina.

And they contain only fruit and vegetables - no ice - although they manage to keep the drinks cool by adding some frozen fruits.

Mr Hallworth added: "Because we are always starting from the same temperature, it is consistent and that is important.

"If someone is buying every morning, they will know the difference if the drink changes."

Mr Hallworth, 35, and his 32-year-old wife came from South Africa four years ago, initially to travel.

They stayed to study nutrition and, while doing so, began mulling over the idea of running a juice bar.

"While we were studying, we were both using the trains," Mrs Hallworth said.

"We were frustrated at not being able to find something healthy on the go."

So when they decided to make their idea a reality, railway stations seemed an obvious place to start.

In addition to juices and smoothies, Vitaburst sells hot juices, fair trade teas and soups (supplied by Portsmouth-based The Soup Ladle) as well as a range of healthy snacks.

The Hallworths use as many organic products as they can, but the fruit and vegetables are generally not organic. "We couldn't find someone who could supply us every day with organic fruit and we want it to be fresh every day," Mr Hallworth said.

Mrs Hallworth added: "I think it would have scared off a lot of people if it had been very expensive. It would have made it a niche market, which we didn't want to do."

However, they are trying to source from local suppliers. Their daily supplies of fruit and veg come from Kingston Fruiterers in Jericho, for example.

After an experimental six months when the Hallworths tried out different combinations, they have gone from strength to strength, managing to make a small profit in their first year.

They are opening their next outlet in Reading because First Great Western asked them to put in a proposal and awarded them the contract.

Mrs Hallworth said: "We offer such a unique product. They don't want any more straight coffee and pastry places."

Prices start at £2.35 for a juice blend, £2.75 for a fruit smoothie and £2.95 for a 12oz super fruit smoothie.

The Hallworths have no plans to return to South Africa, but instead want to expand their empire here.

"We'd like to be a leading juice bar chain throughout the railway networks," Mrs Hallworth said. "Vitaburst is something people can recognise and know. If we have to franchise along the way to do that, it would probably be better, so those stalls can be managed with the enthusiasm that we would put into our own."

But first comes Reading, with the opening due this month.

Mrs Hallworth said: "If there is anything we have learnt from this process, it is that nothing ever goes to plan."

However, given their success so far, it seems they have hit on a winning formula that obviously suits their lifestyle.

In fact, they are a great advertisement for their juice bar concept.

Both are brimming with vitality and positive energy, making you think: "I'll have some of that."

Contact: Vitaburst 07917 095 820.