A warning has been issued that pensioners across Norfolk and north Suffolk could face a cold and miserable winter as a major energy provider announced a massive hike in its prices yesterday.

The warning came from pensioner support groups and charities as British Gas announced its gas prices will rise by an average of 18pc and its electricity bills will increase by an average of 16pc.

The rises, which will come into effect from August 18, make British Gas the second company to announce significant increases in recent weeks. Last month, Scottish Power announced it would raise the cost of gas by 19pc and the cost of electricity by 10pc, and the other energy providers are expected to follow suit.

Organisations in Norfolk and Suffolk that deal with pensioners and vulnerable people have warned of a difficult winter ahead as people struggle to stay warm and also contend with the overall increased cost of living.

Alan MacKim, former chairman and trustee of Age Concern Norfolk, said it would be 'just another nail in the financial coffin' for older people and those on low incomes.

He said they had already been hammered by interest rates and inflation.

He added: 'The fuel prices are another part and besides all that they are having to deal with things costing more. Even if you go to the supermarket everything costs more. It is always hitting older and disabled people.'

The anticipated announcement was made at 10am yesterday - as Prime Minister David Cameron was announcing plans to deal with the News of the World phone-hacking scandal - leading some to speculate it was an attempt to sneak the news out unnoticed.

Mr MacKim described the summer announcement as 'terribly convenient'.

He said: 'Talking about winter and how older people confront this is not the first thing that comes to mind when you are in the middle of summer.

'When winter arrives believe me the effect will be severe, nothing will mask it.'

Pat Wilson, of the Norfolk & Norwich Pensioners Association, described the rise as 'atrocious' and would cause a great deal of worry especially after the budget cut in winter fuel payments for older people.

In March chancellor George Osborne announced that the yearly tax-free payment to help older people pay for their heating in the winter would be reduced from �250 to �200 a week for the over 60s, and from �400 to �300 a week for the over 80s.

Mrs Wilson said: 'Particularly in the colder weather they need the fuel more than other people do as they can't move around as much. I think it will have a disastrous effect on them.'

She said it could be intolerable if there was another cold winter like last year.

'I think a lot of older people will be quite frightened and get very, very worried about how they will cope,' she said.

She added that she was particularly upset by companies that offer online discounts as many older people were unable to take advantage of these.

Emily Millington-Smith, who was made an MBE for services to older people, warned its 'intolerable impact' would only be found out when autumn arrives.

Mrs Millington-Smith, who is president of Age Concern Norfolk and chairman of the Norfolk Older People's Forum, said that some older people will have to decide whether they will only live in one room and keep that heated.

She added: 'We also need to remember people who need warmth and comfort in their homes, like the disabled and people who can't get out.'

The chief executive of the Citizens Advice Bureau Gillian Guy said that their advisors helped almost 104,000 people with fuel debt problems nationwide last year.

Rik Martin, a development manager at Rural Community Council, added that the costs would also be a problem for those who live in rural areas, especially when added to the burden of high fuel prices.

He said: 'Already people in rural communities are being hit by rising transport costs, with fuel poverty quite high. If you live in a rural community all the costs are exacerbated.

'I think there are some serious problems with fuel poverty in Norfolk already and this is just going to make it worse.'

British Gas, which is owned by Centrica, said the hike was in response to a 30pc increase in wholesale prices since last winter, claiming it was currently selling energy at a loss.

It last raised bills by an average of 7pc in December. The latest move means that some bills will increase by as much as 24pc depending on how customers pay and where they live. The minimum increase will be 12pc.

Managing director Phil Bentley said: 'We know there is never a good time to raise prices but we are buying in a global energy market and have to pay the market rate.'

The company said it 'cannot continue to make a loss on the energy it sells' and it needs to make a profit to invest in future energy sources.

In the announcement, it offered numerous ways for its customers to keep their prices down, including fixing their bills or improving insulation in their homes and energy monitors.

Earlier this month gas and electricity watchdog Ofgem announced that it would conduct an investigation into the pricing practices of the UK's big six energy suppliers, after it emerged that movements in household bill rates bear little relation to the wholesale costs paid by the firms.