Ed Miliband's personal ratings among Labour supporters have reached the highest levels since 2010 following his crowd pleasing call to freeze energy prices during the Labour party conference.

But Miliband's boost among party loyalists has not translated into a larger Labour lead with the Ipsos Mori poll now putting the two parties neck and neck on 35%.

Satisfaction with Miliband's leadership has risen by 12 points — and by an impressive 21 points among Labour supporters, since he burnished his credentials among the left of the party. The poll also shows an increase in the number of voters who see him as leftwing or left of centre.

Downing Street believes the energy price policy although popular, is not seen as credible by voters, perhaps explaining why the uplift in Miliband's personal ratings has not translated into a hardening of the Labour lead. Some 62% in the poll said Labour's energy price freeze would be the best policy for them personally, while only half said it would be best for the country.

Downing Street also said the improvement in the economy is slowly feeding into gains for the Conservatives. A YouGov poll earlier this week also had the two parties on the same figure.

The Ipsos Mori poll shows that among all voters 36% are satisfied with Miliband's leadership, and 49% dissatisfied, a net negative of 13 points, but a 23-point improvement on his previous rating. Miliband now has a better net satisfaction rating amongst general voters than David Cameron.

Miliband continued the populist flavour of his recent politics by announcing that lenders such as Wonga face a possible 10% tax on profits under a planned crackdown on payday lenders.

Miliband has vowed to "call time" on the "exorbitant" interest rates charged by some firms, which can see borrowers end up paying thousands for loans that were initially in the low hundreds of pounds.

A Labour government would impose a new levy on payday lenders to fund a £13m increase in public support for low-cost alternatives, such as credit unions.

Responding to the Labour party's proposals, Russell Hamblin-Boone, chief executive of the Consumer Finance Association, which represents short-term lenders, said his industry had not been consulted on the plans and was keen to see the detail. He added: "We fully support the important role that credit unions play in ensuring that people have a choice of financial products to meet their needs, but they provide very different services to our members.

"Payday loans are small sum, short-term loans and should not be used to manage long-term debt. We already support a range of debt advice organisations, as part of our responsible lending practices."Labour also confirmed that it was to give councils greater powers to stop pay day lenders opening shops in high streets and repeated its promise to impose a cap on the cost of credit.

Miliband said: "We've got a cost of living crisis in this country and it's driving people into the arms of payday lenders and causing them untold hardship.

"We are saying that we want payback from these payday lenders so we want to force them to fund low-cost lending which can actually help families and communities rather than harm them, which is what so many payday lenders are doing.

"The government has just been too slow to act and has been dragging its feet and not standing up to the payday lenders. That's why Labour would have a cap on the cost of credit."

"Someone has got to call time on it," Miliband said during a visit to a credit union in Peckham, south London. "That's what a Labour government will do."

Payday lenders, which offer short-term loans to tide over customers who run out of money while waiting for their monthly pay cheque, have been widely criticised for charging vulnerable individuals sky-high interest rates which can top 5,000% a year.

Companies will any way pay an existing levy when they start being regulated by the Financial Conduct Authority (FCA) next April, but Labour is proposing an additional charge on top of this to boost the credit union market, where loans are available at much lower rates to households unable to access the mainstream credit market. Labour said it would raise about £20m a year from controversial lenders such as Wonga – either from a 1% levy on their balance sheet or a 10% profits tax.

A cap on the cost of credit was included by the government in the bill establishing the FCA, but has not yet been implemented.

The FCA in a consultation paper in October said they do not have the data from lenders to set a proportionate cap. It has also suggested evidence for its success abroad is mixed. Stella Creasey, the new shadow consumer affairs minister and a long term advocate of a cap, has said the government must step in before April 2014 to make it a requirement for these companies to work with the FCA in setting a proportionate cap.

The FCA has instead promised to impose tighter affordability checks, and limiting the use of rollovers and continuous payment authorities.