Nearly a third of all energy companies fitting smart meters are still installing old technology.
Government guidance says that since the middle of March 2019 customers should only have been given second generation smart meters.
However, eight companies still installing first generation smart meters say the network is not reliable enough to switch customers on to.
They say this is particularly a problem in northern England and Scotland.
The auto-switching service Look After My Bills has discovered that Bristol Energy, British Gas, Ecotricity, EON and Octopus are still installing some first generation meters in the North, and Nabuh Energy, Simplicity and Utilita are only installing the first generation after encountering difficulties with the new system.
The second generation of meters is supposed to be able to connect remotely to a national network, which should make switching supplier possible, for the first time for many customers.
When contacted by the BBC, the companies emphasised that the issues were industry-wide problems.
"We are not ignoring government guidance," said a spokesperson for Ecotricity. "In fact it's clear that in documented instances where a SMETS2 meter cannot be used, or in areas where connection is not possible, we are encouraged to use SMETS1, or non-smart meters."
Two different contracts were given out by the government to install those networks. The Southern Communications Network is being run on pre-existing mobile technology, while the Northern Communications Network is being run via specialist radio signal.
A number of the companies claim that problems with the signal in that Northern Communications Network mean that they cannot reliably connect customers to it. Therefore customers living in the South of England and Wales are much more likely to receive a second generation meter, than those living in the North of England and Scotland.
Octopus energy said the priority was to ensure customers' needs were met.
"Where a second generation meter can be reliably installed and commissioned, we'll do that," the firm said. "Otherwise we'll offer customers the choice between first generation or waiting until second generation is available."
Some firms also highlighted problems with the connection in high-rise flats and for those on pre-payment meters.
The company responsible for the operation of the data networks across the UK, Smart DCC, said thousands of second generation meters were being installed in the North every day.
"DCC is supporting the energy industry as it rolls out second-generation smart meters across the country," it said. "There are now more than two million operating on our smart, secure network," Smart DCC said.
Utilita supplies energy almost exclusively to pre-payment customers. The firm said it is waiting for the result of a judicial review into government policy, as it says companies should not be compelled to install the new meters.
Utilita believes the new system has significant connectivity problems and "provides a vastly inferior service for pay-as-you-go customers, many of whom are vulnerable".
Bristol Energy said any installations of SMETS1 meters since March have been because customers are on pre-payment meters.
"As part of our social purpose, we have a fair proportion of customers who are in this payment category," it said.
British Gas agrees, adding there "have been some industry-wide delays with the infrastructure for SMETS2 pre-payment meters which means we're not yet installing SMETS2 to all of these customers."
Simplicity energy said it is waiting for the first generation meters to have an upgrade, rather than install the newer version, which it believes will happen shortly. The firm said: "Our strategy is to complete our roll-out programme and run down our stocks of SMETS1 meters to avoid them becoming landfill."
Any first-generation meters installed after 15 March 2019 do not count towards the companies' smart meter roll-out obligations, and the regulator, Ofgem, could take enforcement action against any company not meeting those obligations.
The Department for Business, Energy and Industrial Strategy said "the network for the North is fully operational, with thousands of second generation meters being installed every day.
"Smart meters provide a much better service for customers over traditional meters. This is particularly the case for pre-payment customers by cutting costs," it added.