TaxPayers' Alliance political director Jonathan Isaby says the principle of simplifying the benefits system is right but the implementation is "deeply flawed".
He added: "A horrendous amount of taxpayers' money has already been wasted and those responsible for that must be held to account.
"Such a fundamental reform of the welfare system was always going to be a challenge, but the approach of many officials in the Department for Work and Pensions has been little short of shambolic."
More top news
A man has been charged with stealing his own barrister's mobile phone at a magistrates' court in Bexleyheath, Kent.
A rapist who attacked an 80-year-old woman in her own home has been jailed for life, as police urge other victims to come forward.
Sunniest April on record - how's May looking?