The shadow chancellor has said he believes in a low tax economy, but did not make any specific commitment to cut taxes in a speech today.
The Conservatives say they are unable to make specific policies on tax cuts until they know for sure the exact state of the public finances. They claim that Labour's spending plans are unaffordable without a taxation rise.
In his speech this afternoon, Oliver Letwin committed his party to safeguarding education and health, but promised to end "fat government" and begin lasting reform of the tax system.
This summer, the Conservatives have unveiled the results of the James Review, which they claim has identified billions of pounds worth of savings in government.
Mr Letwin said: "By thinning down fat government we can stick to my tight spending controls and yet fund public services properly.
"And those tight spending controls will enable us to prevent Labour's third term tax rises. They should be enough to enable us to do more. They should be enough to enable us to do something serious to make Britain's tax system simpler and fairer."
He added: "There have been too many broken promises on tax from too many politicians. When we were in office we made promises on tax we could not keep. And everybody knows what happened when Tony Blair promised that he had no plans to increase taxes at all - and then raised taxes 66 times by stealth. So no more broken promises on tax."
He did promise to freeze civil service recruitment and remove controls on local government.
Mr Letwin is also promised reform of the council tax, inheritance tax, stamp duty, income tax and National Insurance thresholds and the taxation of savings and pensions.
Capital gains tax, small business taxation and environmental taxes were also be identified as "over complicated".
The shadow chancellor branded a rising tax burden and increases in government bureaucracy "morally wrong" and promised to work for a simpler tax system.
© DeHavilland Information Services plc