As attention turns towards Budget day the Conservatives have accused the chancellor of creating an over-complex tax system.

Shadow chancellor Michael Howard argued on Friday that Gordon Brown has used a web of tax credits and direct levies to increase the burden of taxation.

"It is little wonder that one of the most serious criticisms that can be levelled against the chancellor is the increasing complexity of the tax system. The Institute of Chartered Accountants, for example, has said that the tax system has 'spun out of democratic control' because of complexity, the number of anomalies and the 'culture of never-ending change," he said.

He argued that Gordon Brown is using complex methods to hide the true cost of his Budgets and the details in his annual speech are becoming increasingly complex.

"The government has deliberately excluded the impact of indirect taxes when illustrating the effects of Budget changes on specimen households. The public accounts themselves are now more opaque and confusing than for many years.

"The Budget Red Book has been transformed from a coherent document that lucidly explained economic policy to a discursive document that confuses more than it informs. Meanwhile its length has risen from 160 pages when we left office to 225 pages last year. The Finance Bill likewise has risen from 219 pages to 292 pages," he said.

He also called for a US-style parliamentary agency to analyse Gordon Brown's tax and spending decisions.

Currently the two main checks on the Treasury are the National Audit Office, which oversees all the government departments, and the Treasury select committee.

In a speech to the Centre for Policy Studies, he said that the chancellor's fiscal rules are no more than a rule of thumb and call for changes to make them more meaningful.

"One possibility would be to equip parliament with an agency that could offer serious analysis of spending, borrowing and taxation in a manner comparable to that achieved by the Congressional Budget Office in the United States," he said.

"It would mean that all the Treasury decisions could be authoritatively challenged by an objective agency accountable to parliament. Additional scrutiny could also help achieve transparency."

Howard claimed the most important issue as far as the public is concerned is not how much money is being pumped into public services - such as health - but how it is spent.

"Fiscal rules - like the government's objective of raising health spending to the European average - relate only to inputs into the public spending equation," he said.

"Yet the most important issue is the outcome of that spending - its effectiveness. There needs to be a rigorous approach to assessing the effectiveness of decisions about public spending and investment. Need for value for money in assessing public spending."

Howard also said that there was now a clear consensus between the government and the Conservatives over economic policy.

"In monetary policy at least, there is now a very considerable degree of economic consensus. That consensus, and the stability and continuity which spring from it in economic affairs, is greatly to the advantage of our economy and is a matter for celebration," he said.

But Howard warned that Labour was storing up trouble for the economy, which would eventually fall behind European rivals.

"The combination of ever-higher taxes along with ever worsening public services, a less transparent tax system and employment regulations that make the labour market less flexible will, in the medium-term, depress the economy's growth rate."