Train company c2c has unveiled the country's first part-time season-ticket for its Essex to London routes, in a move that could save commuters more than £100 a year.

If you work less than five days a week and travel with c2c, which services parts of Essex (from Shoeburyness to London Fenchurch Street), you'll now be able to buy a 'Flexi-Season' ticket, saving an average of 5% on the cost of an anytime day return ticket.

When you buy a Flexi-Season you actually get 10 tickets – one of those tickets lasts for a whole day of travel on your chosen c2c route – though they expire after 26 weeks (that's about six months).

How much you save depends on your particular journey, with part-time commuters from Southend potentially saving upwards of £135 on their annual train expenses.

Read our guide to find out how to buy cheap train tickets.

How does a c2c Flexi-Season ticket work?

Flexi-Season tickets are bought online and then loaded onto a c2c Smartcard (its version of the Oyster card you'd use to travel around London), so you'll have to have one of those to benefit. To use a c2c Smartcard (which are free and can also be ordered online) you simply tap it on the card reader at station barriers.

Each of the 10 tickets you get with the Flexi-Season works like a day travelcard, allowing you to travel as much as you like between your chosen destinations on the day you use each ticket.

You can only buy Flexi-Season tickets in increments of 10, but your c2c Smartcard can hold up to 50 at one time.

Is it cheaper?

c2c says each ticket in a Flexi-Season is about 5% cheaper on average than the equivalent anytime day return ticket, if it's used at peak times.

However, it admits that on journeys between London Fenchurch Street and stations outside the London Travelcard area, the savings may be as low as 2%.

On all other journeys Flexi-Season tickets are between 4% and 27% cheaper than the equivalent anytime day return ticket, depending on the journey and the route.

But there's an extra saving on offer if you use your Flexi-Season tickets at off-peak times, or on weekends and bank holidays.

If you travel off-peak you'll get an additional 10% on top of the first saving. This is applied as credit to your online c2c account, and can be used against future purchases. It's calculated as 10% of the cost of that day's travel.

And if you travel super off-peak (weekends or bank holidays) you'll get back the difference between the cost of your Flexi-Season ticket and that of a weekend off-peak return ticket. This is also credited to your c2c account.

What are some typical savings?

Based on commuting to London Fenchurch Street three days a week, those from Basildon could save more than £100, from Benfleet almost £125 and from Southend more than £135 by purchasing Flexi-Season tickets instead of anytime day returns.

Could full-time workers save too? found that on some routes the Flexi-Season also works out cheaper for full-time workers than buying a weekly season ticket – but ONLY in specific circumstances.

For example, if you commute from Basildon to London Fenchurch Street at peak times, five days a week, a weekly season costs you £67.70, but a Flexi-Season works out at £65.55 per week.

And if you're a full-time worker commuting from Purfleet, a weekly season costs £56.40, whereas a Flexi-Season works out at £54.64.

However, that's not the case for all routes – for example, full-time peak commuters from Southend Central will find the weekly season for that route cheaper than the Flexi-Season.

And it's worth remembering that weekly season tickets last for seven days, so if you're a full-timer and use yours to travel at the weekend too you're probably better off with it than you would be with a Flexi-Season.

How can I check whether I'll save with a Flexi-Season?

You can compare a Flexi-Season against the cost of an anytime day return and a weekly season ticket using this calculator to see if you'll save.

Monthly or annual season tickets may still offer the biggest savings of all if you're a full-time worker and peak-hours commuter. The best option for you will vary according to your route and how often you travel.

Is this really the first part-time season ticket available?

It is indeed. They're already in use in some European countries, and the UK Government first announced plans for them back in 2012.

Last year Martin Abrams from the Campaign for Better Transport called for more to be done to make fares fairer for part-time workers.

The UK has some of the highest rail fares of any European country.