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Downing Street has dismissed calls to delay the introduction of the universal credit benefit system.

A spokesman said the project, being pushed through by Work and Pensions Secretary Iain Duncan Smith, was "on track and on time".

He said: "It is a vital part of our welfare reform agenda and we are fully committed to it."

Seventy organisations have raised concerns about new monthly payments, access to an online system and IT.

The universal credit will replace jobseeker's allowance, tax credits, income support, employment and support allowance - formerly known as incapacity benefit - and housing benefits with a single payment.

The system will be "piloted" in parts of north-east England next April and will come into force nationally for new claimants from October 2013. Existing claimants will be transferred to the new system in stages until 2017.

Written evidence, seen by ´óÏó´«Ã½ Radio 4's The World This Weekend programme, was submitted to the House of Commons Work and Pensions Committee by 70 organisations representing councils, charities, trades unions, businesses and housing groups.

The Women's Budget Group and the singe parents' group Gingerbread raised concerns over the effect of monthly, rather than fortnightly, payments on household budgets.

The Local Government Association, meanwhile, was among those concerned there was "a real risk that the central government universal credit IT systems will not be ready on time".

Pressed on whether the October 2013 start date for the new benefit could be put back, the Downing Street spokesman said: "It's on track to be implemented in that timetable."

Mr Duncan Smith is currently appearing before the Commons Work and Pensions Select Committee.

He told members he was confident that the target of 50% of benefit claims being made online by 2013 could be met.