Backlogs are still being reduced too slowly more than a year after Home Secretary Theresa May moved to deal with a string of fiascos by bringing immigration back under ministerial control and boosting resources, a public spending watchdog warned.

The National Audit Office found the service continued to be plagued by poor IT, weak workforce planning and low morale despite the decision to abolish the UK Border Agency in favour of direct Home Office control in March last year.

While the switch had resulted in some improvements, it found, in some key areas it had "not progressed as far as we would have expected".

The chairwoman of the Commons public accounts committee Margaret Hodge expressed frustration at the slow pace of change, especially the failure to improve data after a £347 million IT system failed to bring all the benefits it was supposed to.

The Labour MP said it was "simply not good enough" that the Home Office was not able to say where it had shaved almost £6m from its budget, leading the NAO to warn services could be at risk from future spending cuts.

Ms May abolished the UKBA and replaced it with UK Visas and Immigration and an Immigration Enforcement command.

The NAO said that while all "straightforward" cases had been cleared, there were still 301,000 open cases -including more than 25,000 live asylum claims.

Catching up was hampered by using "multiple and complicated legacy systems".