LONDON, April 21 (Reuters) - Britain said on Thursday all 37 car models it had tested exceeded the laboratory limits for polluting nitrogen oxides during real-world driving, but only Volkswagen had used so-called defeat devices to cheat tests.

The transport ministry said it tested models from all major carmakers. It tested 18 older cars against so-called Euro 5 standards for nitrogen oxide (NOx) levels and 19 newer ones against tougher Euro 6 levels, with all the vehicles recording readings above the legislative limit during on-road tests.

“It can be seen that all of the results are substantially higher than this limit, with the best results being about three times higher, and the worst about ten times higher,” it said, referring to vehicles tested against Euro 5 levels.

The ministry said carmakers had “not done anything illegal” as they only had to meet laboratory standards at present.

Britain launched an investigation into emissions after German carmaker Volkswagen (VW) admitted to rigging U.S. diesel emissions tests in September.

Britain said real-world driving emissions tests would be introduced from 2017.

On Thursday, the Department for Transport said only VW had been found to be using defeat device software to cheat tests.

“The vehicles tested in the UK programme showed no evidence of car manufacturers, apart from VW Group, fitting devices to defeat the approved emissions test programme,” it said.

VW had previously said 1.2 million of its models in Britain had been fitted with defeat devices. It saw its UK sales plummet from October. They returned to growth in March, edging up 0.02 percent.

The ministry said it cost 1 million pounds ($1.4 million) to re-test the vehicles and that Germany would soon be publishing results of its own testing of 56 vehicles.