Vector profits for the first half of the financial year rose 6.9 per cent, despite revenue growth of just 0.8 per cent.

Profits for the first half of the year have slumped at Contact Energy, the stock exchange's largest energy company.

Mercury Energy is raising its power prices by 5.8pc, blaming charges from the national grid operator Transpower.

One in four households switched power retailers in search of a better deal last year, according to Powershop.