For Immediate Release 12 May 2008 Portland Gas PRESS RELEASE Strategic Partner joins the Larne project The Directors of Portland Gas plc (AIM: PTG) ('the Company' or 'Portland Gas') are pleased to announce that its Northern Ireland subsidiary Portland Gas NI Limited has agreed Heads of Terms with Moyle Energy Investments Limited, a subsidiary of Northern Ireland Energy Holdings Limited ('NIEH'), operator of the Scotland to Northern Ireland Pipeline (SNIP), for NIEH to participate in the Larne Lough gas storage project. Under the terms of the agreement NIEH have an option, following completion of a due diligence process and consultation with their stakeholders, to become a joint venture partner taking a 35% equity interest in the Larne Lough project and paying their share of the development costs. Commenting on the project Andrew Hindle, CEO of Portland Gas plc, said: 'NIEH have been assisting Portland Gas for over a year and their involvement is integral to the success of this strategically important project. They own the gas infrastructure into which the Larne Lough gas storage project would be connected. With their long-term approach and intimate understanding of local customer, regulatory and government needs, the mutual energy infrastructure company is an ideal partner for Portland Gas NI Limited.' For further information please contact: Portland Gas plc Andrew Hindle, Chief Executive Officer 020 8332 1200 Craig Gouws, Chief Financial Officer Investor Relations - Buchanan Communications 020 7466 5000 Ben Willey Corporate PR - Watershed 01308 420785 Sara Hudston Jet PR (Northern Ireland Public Relations Consultant) 07803 722322 Jacqui Thompson Nominated Advisor and Broker - Seymour Pierce 020 7107 8000 Jonathan Wright Notes to Editors: Background on Portland Gas plc Portland's business focuses on the development of gas storage projects in the United Kingdom and internationally. It currently has two projects in its portfolio: an advanced project on Portland, Dorset, which has been under development for over three years, and the Larne Lough project in Northern Ireland, which was announced in July 2007. Further information is available on the Company's website www.portland-gas.com. Background on Northern Ireland Energy Holdings ('NIEH') NIEH is a company limited by guarantee. Its principal objective is to own and operate energy infrastructure assets in the interests of the energy consumers of Northern Ireland. The company is a mutualised entity and therefore has no shareholders and its primary stakeholders are energy consumers. NIEH subsidiary Premier Transmission Limited operates the Scotland to Northern Ireland natural gas transmission pipeline ('SNIP'). The 24-inch diameter pipeline is 135 kilometres long and runs from Twynholm in Scotland to Ballylumford in Northern Ireland. It transports gas to Ballylumford Power Station which generates over half of Northern Ireland's electricity needs and feeds the natural gas distribution system in Belfast and the Greater Belfast area. NIEH also operates the 500 megawatt Moyle interconnector to Scotland. Background on the Larne project The interpretation of a 3D seismic data acquired in 2007 has indicated that the Permian salt sequence encountered in 1981 in the Larne-2 borehole extends under Larne Lough into the area where Portland Gas was granted an exploration licence in 2007 by The Crown Estate. The salt in the target area is at a depth of approximately 1,400 metres with a thickness of approximately 200 meters. Portland Gas is planning to drill a borehole later in 2008 on Islandmagee to confirm the seismic interpretation and to take cores of the salt sequence to complete the design of the caverns to store natural gas. The Company is seeking a suitable site from which to drill the borehole within the area of its onshore mineral licence, awarded in 2007 near Ballylumford by the Department of Enterprise, Trade and Investment. Portland Gas is undertaking an Environmental Impact Assessment with the intention of submitting a full planning application for the gas storage project in 2009, subject to concluding any necessary landowner agreements. The Company will liaise closely during 2008 with all stakeholders to ensure that the surface facilities, required to create the caverns and compress the gas into store, are located in the most appropriate place and designed to minimise visual and environmental impact. The caverns would be created within the salt sequence below Larne Lough but accessed from directionally drilled boreholes on the land. The nearest point of connection to the national gas infrastructure is at the Scotland to Northern Ireland Pipeline above ground installation at Ballylumford. Network, market, technical and economic analyses are also underway to determine the most appropriate storage capacity and the gas injection and withdrawal rates for the facility. Initial studies indicate that the facility could have a storage volume of up to 500 million cubic metres (18 billion cubic feet) of gas. In this case some reinforcement of the current gas infrastructure will be required to manage the injection and withdrawal of gas and provide sufficient flexibility to meet demand spikes for customers. Background to gas storage Natural gas is an extremely important source of energy, currently contributing 39 per cent of the UK's energy needs. For many years, the UK has relied heavily on its North Sea gas fields. That resource of secure and sustainable gas flow has limited the need to provide significant storage volumes since daily and seasonal demands for gas have been accommodated by the flexibility of supplies close to shore. This relative luxury is becoming less and less sustainable as the UK becomes increasingly reliant on less flexible imported gas, the outcome of which is that in order to maintain control of supply and demand requirements, the need for a substantial portfolio of natural gas storage facilities is now a national issue. Gas storage plays an important role in managing swing demand and mitigating the need for (expensive) emergency imports. Gas storage facilities can be filled during times of lower demand to be available during periods of higher demand, either on a daily basis or seasonally. Opportunities for a safe and environmentally friendly method of storing gas are relatively few. One of the safest and most environmentally friendly methods of storing large quantities of gas is deep underground within caverns created within salt sequences. This is a tried and tested method in use all over the world for more than 40 years.