Consumers in and around Northern Ireland's capital city can choose who supplies their domestic gas, with competition in the market opening up for the first time ever.

Firmus Energy is now competing against previous monopoly provider Phoenix Natural Gas to the Greater Belfast area but not the rest of the territory (see our Cheap Heating Oil guide for tips on cutting costs).

For the fourteen years since its inception, Phoenix had been the only supplier of natural gas to domestic properties in Greater Belfast and the surrounding area until this year. It supplies 130,000 homes and businesses.

While competition opened up in the business gas market around five years ago, the domestic market has been slow to follow.

However, following a trial period from November 2010, Firmus has now fully launched into the Greater Belfast domestic market following approval from Northern Ireland's Utility Regulator.

Firmus, until now, only supplied natural gas in the domestic market to areas close to a pipeline that runs between Londonderry to Newry, plus the northern tip of the country, after being awarded a licence to do so in 2005. There is no competition in those regions as it is the only supplier.

By switching to Firmus, where there is competition, those who currently pay Phoenix by cash, cheque or direct debit will pay 7.5% less in year one and 5% less in year two than its standard published rates (discounting the direct debit discount).

To get those discounts, consumers must pay by direct debit, choose online billing, send quarterly meter readings and apply by December 2011. Pay as you go customers will be eligible for the deal from September 2011.

A Firmus spokeswoman says: "Customers switching to Firmus can be assured that, as we will be tracking Phoenix prices for at least the next two years, they will continue to pay lower gas prices no matter what Phoenix charges."

Yet Phoenix insists it is not concerned by the competition. A spokesperson says the introduction of Firmus Energy into the domestic gas market will be "positive for consumers" and "encourage more people to use gas", as well as being beneficial for Phoenix as Firmus uses its pipelines.

Mark Todd, of price comparison site, says the move is "good to introduce some competition".

If you are considering switching to gas or want to change providers you can visit either the Firmus or Phoenix website.

The infrastructure to supply natural gas in Northern Ireland is unlike that in the rest of the UK. Around 70% of its population still use home heating oil rather than gas.

There has been competition in the Northern Ireland electricity market since last summer.

Further reading/Key links

Cheap energy guide: How to switch and save