BORD Gais customers currently paying half price for gas would be better off remaining at their current rates than changing to the company's new payment plan. About 10,000 of the company's 250,000 customers currently pay for their gas at the 50/50 Cashback rate.

For other customers, who now have an option to change to the company's new payment plan, the advantages of a reduction of up to 24 per cent in the charge per kilowatt of gas, used will have to be weighed against the introduction of a new annual supply charge of £132. Customers using what Bord Gais claims is the average of 21,000 kilowatts at the most common Supersaver rate would lose out by almost £15 a year by switching to the new system.

Bord Gals estimates about one third of its customers would benefit by transferring to the new payment structure.

In a market development drive, Bord Gais is changing its complicated tariff structure for new customers. Existing customers can choose to change to the new structure or remain at their current rates.

The change in the tariff structure is aimed at simplifying the system and at improving access to gas for many potential customers for whom the £630 connection fee (central heating customers) was prohibitive, according to Bord Gals. A spokeswoman said the new payment rate was aimed at new residential customers.

Bord Gais currently has a complicated payments structure with four payment rates which are related to gas usage. The new system involves a standing charge of £22 per two month billing period (£132 a year) plus a charge for gas at a rate of 1.75p (including value added tax) per kilowatt used.

The new 1.75p/kW charge is 24 per cent lower than the current lowest rate for customers not benefiting under the half price 50/50 Cashback scheme. But the new supply charge - will add £132 to the annual bill of existing gas users who opt for the new system.

New customers will pay a lower rate for gas used but will have to pay the annual £132 supply charge. They will not pay any connection fee and will face no minimum consumption commitments.

Under present arrangements, existing customers must pay levies on their annual bills if they fail to meet minimum consumption commitments - effectively a minimum charge tied to the price at which the gas is supplied.

Existing customers pay for gas at rates of between 2.303p to 4.606p/kW (including VAT) depending on the amount of gas used. Some 10,000 benefit from 50/50 Cashback the Bord Gals promotion which offered half price gas for a three year period to customers who installed gas central heating systems. This promotion ended in December.

There are four payment rates for existing customers.

The Supersaver rate, which applies to about 70 per cent of customers, involves a commitment to use a minimum of 16,000 kilowatts a year and the charge, is 2.303p/kW (including VAT).

Customers on the Supersaver rate and using more than 24,000 kilowatts would benefit by changing to the new system. For example, a customer using 25,000 kilowatts a year pays £575.75 under the existing system. Under the new system that customer would pay £569.50, a saving of £6.25. But if the customer currently has the 50/50, Cashback rate the annual bill would be only £287.88. That customer should then remain on the 50/50 rate until it expires and then change to the new payment system.

A customer using 40,000 kilowatts now has an annual bill of £921.20, or £460.60 if the Cashback rate applies. Under the new system the bill would be £832, a saving of £89.20 for a customer on the Supersaver rate. But customers with the Cashback advantage would see their annual bills rise by £371.40. Typical consumption on the Supersaver rate is 21,000 kilowatts a year, according to Bord Gais.

Another of the four payment rates is the economy rate of 3.032p/kW. It requires a minimum annual consumption of 8,750kWs - effectively a minimum charge of £265. The double up rate of 3.839p/kW requires a minimum annual usage of 5,850kWs or a minimum charge of £225. Customers on the reducing rate pay different rates through the year as their consumption rises, starting at 4.606p/ kW and possibly falling to 2.442p/kw.