* UK price cap to lead to 300 mln stg hit in 2019
* British Gas lost 742,000 customers in 2018
* Operating profit up 12 pct in 2018
* FY dividend maintained at 12 pence
By Susanna Twidale
LONDON, Feb 21 (Reuters) - Shares in British Gas parent Centrica (Frankfurt: A0DK6K - news) slumped to a 16-year low on Thursday after the group warned a national price cap on energy bills, a fall in nuclear output and lower volumes at its oil and gas division would hit its 2019 results.
Centrica said a regulator-imposed cap on standard energy prices would lead to a 300 million pound ($392 million) hit to profits in 2019, including a one-off impact of about 70 million in the first quarter of 2019.
Late last year Centrica, whose British Gas unit is Britain's largest energy supplier, said it would seek a judicial review of the way regulator Ofgem calculated part of the price cap, which was initially set around 6 percent lower than British Gas's standard variable tariff.
Ofgem this month said the cap will be raised by 10 percent from April 1 and British Gas has already said it will increase its prices by the same amount.
"We believe (the cap) is the wrong intervention but it is here and we will live with it," Chief Executive Iain Conn told journalists.
British Gas shed 742,000 customer accounts in 2018 as the company came under pressure from smaller, nimbler rivals, often able to offer cheaper deals.
Centrica posted a 12 percent rise in 2018 operating profit to 1.39 billion pounds, bolstered by higher commodity prices, and maintained its full-year dividend at 12 pence. But traders focused on the weak outlook and concerns the dividend could be under threat in future.
"Although a much-feared reduction in Centrica's dividend hasn't been explicitly announced today, the writing is pretty much on the wall," said Cityindex senior market analyst Fiona Cincotta.
Shares were down 11 percent at 122.15 pence by 1038 GMT, having touched a 16-year low of 120.05p.
In exploration and production, volumes at Centrica's Spirit Energy are expected to remain in the lower half of its 45 to 55 million barrels of oil equivalent range for 2019.
Meanwhile, output from the company's 20 percent stake in Britain's nuclear plants was still affected by current outages, Centrica said.
The company is targeting sales of 500 million pounds from the sale of non-core assets in 2019 and said it would sell Clockwork Inc, its North American home services business, for $300 million.
Conn said plans to sell its UK nuclear stake are ongoing and the company expects to provide an update on this mid-year.
It also plans to make efficiency savings of around 250 million pounds, include making between 1,500 and 2,000 job losses on a like-for-like basis in 2019, which Conn said were part of the 4,000 cuts to 2020 announced last year. ($1 = 0.7669 pounds) (Reporting by Susanna Twidale in London Additional reporting by Devika Syamnath in Bengaluru Editing by Emelia Sithole-Matarise and David Holmes)