RTÉ has announced that it is ceasing the long wave 252 service for Radio 1 from next month.
The move was originally announced in 2014 but was postponed because of protests from Irish organisations in Britain.
RTÉ said in a statement that the LW 252 is no longer sustainable as the transmitter in Summerhill, Co Meath uses up 2.5% of the organisation's energy use.
The current cost is €250,000 a year and this could rise to €400,000 next year, it says.
When the move was announced originally there were complaints from Irish people in Britain, particularly the elderly, who would no longer be able to get RTÉ Radio 1 on their transistor radios.
The closure was deferred - initially for three years - but the long wave service will now end on Friday 14 April.
However Radio 1 will be available in Britain to listeners on Freesat (channel 750), Sky (channel 0137) and Virgin Media (channel 917 - but that may vary depending on the Virgin Media set-top box).
It will also be available on streaming devices including RTÉ Radio Player and Irish Radio player apps.
In Ireland it will continue to be available on FM as well as through TV channels and online.
An information campaign will see advertisements in Irish newspapers in Britain as well as flyers and posters, which will be distributed through Irish organisations there.
RTÉ Director General Dee Forbes said that continued investment in prolonging the long wave transmitter can no longer be justified.
"Not only is RTÉ Radio 1 widely available in the UK across television and online services, including apps and smart speakers, the energy costs involved along with the cost of replacing the transmitter mean that, in line with the recommendation of the Future of Media Commission Report, the time has come to bring the long wave service to a close," Ms Forbes said.
In its statement RTÉ said long wave is not readily available on modern radio sets or audio systems and there are few such services remaining in Europe - the BBC has announced the closure of its Radio 4 LW service.
Ending the service will also bring a reduction in RTÉ's carbon emissions, it said.
The Summerhill transmitter will be shut down but there are no plans to physically dismantle it.
Information on how to continue to listen to RTÉ Radio 1 in Ireland or in the UK is available on www.rte.ie/keeplistening.
RTÉ said its Information Office is available to answer questions regarding the Long Wave service on +353 12083434 or at email@example.com