Sweltering conditions on Boris Johnson's new Routemaster-style buses are rising beyond the legal limit for transporting livestock, a secret study by Transport for London has confirmed.

TfL checks, released under freedom of information to Politics.co.uk, found temperatures of up to 34 degrees centigrade on the top decks of some buses, with air conditioning units failing to make conditions on the buses comfortable.

On a number of buses, faulty air conditioning units were found to be "blowing hot air" into the bus, raising temperatures well above the legal limit for transporting livestock, currently set at 30 degrees.

Checks carried out by technicians at one location in central London in August found "uncomfortable" conditions on the top decks of almost 60% of buses they measured.

The internal report confirms figures released to Politics.co.uk last month showing a surge in the number of public complaints about heat on the buses.

Up to 15 formal complaints about "Sauna-like" conditions on the buses were received a day by TfL in June and July this year.

A spokesperson for Transport for London said they had identified just eight buses with faulty air conditioning, but insisted that air conditioning on the vast majority of buses was working as intended.

However, TfL's own study found that technicians recorded uncomfortable conditions even on those buses where the air conditioning was operating at its full capacity.

"Pretending that there is not a problem with the new bus for London is simply not an option for the Mayor and TfL," Liberal Democrat London Assembly member Caroline Pidgeon told Politics.co.uk.

"Transport for London's excuses for excessive heat levels on the incredibly expensive new 'Routemaster' buses are rather like the hot air that bus passengers have to endure,"

"If there are faults with the air conditioning of even eight buses that is a significant problem in a relatively small bus fleet.

"However, the fundamental issue is that even when air conditioning is working temperature levels are still excessive."

TfL today insisted that the recorded conditions were due to hot weather and that any faults with the buses were being fixed.

"Eight vehicles were found to have a faulty cooling system. These vehicles were reported to the operator immediately who instigated investigations and repairs," a spokesperson said.

"Additionally there were vehicles that were reported as warm although the system was functioning as designed. There may have been a number of reasons for this, for example, the bus has been on its stand in direct sunlight and the cooler has not been running long enough to bring down the temperature at the point when the check was conducted," they added.