Immigration rules are “overly complex and unworkable” according to the Law Commission, which recommends simplifying them in order to save the government £70m over the next decade.

The regulations have quadrupled in length since 2010 and are “comprehensively criticised for being poorly drafted”, says the body, which advises ministers on updating the law.

When introduced in 1973, immigration rules ran to 40 pages; they now extend across 1,100. Making them more prescriptive was intended to produce more transparent outcomes but instead rendered them harder to follow, the study observes.

Nicholas Paines QC, the public law commissioner, said: “For both applicants and case workers, the drafting of the immigration rules and frequent updates makes them too difficult to follow. This has resulted in mistakes that waste time and cost taxpayer money.

“By improving the drafting, restructuring the layout and removing inconsistencies, our recommendations will make a real difference by saving money and increasing public confidence in the rules.”

The need for clarity has become more acute, the Law Commission heard in evidence it received, because more and more applicants are unrepresented and struggle to understand proceedings.

Immigration regulations have an impact on millions of lives every year, the report accepts. “Their structure is confusing and numbering inconsistent. Provisions overlap with identical or near identical wording. The drafting style, often including multiple cross-references, can be impenetrable. The frequency of change fuels complexity.”

The report adds: “It is a basic principle of the rule of law that applicants should understand the requirements they need to fulfil … For the Home Office, benefits include better and speedier decision-making.

“This leads to a potential reduction in administrative reviews, appeals and judicial reviews, and to a system which is easier and cheaper to maintain.” Reforms could result in savings of almost £70m over the next 10 years.

The report recommends a complete redrafting of the rules, dividing them up by subject matter and limiting the number of updates to twice a year.

Many applicants have little confidence in the system, the Law Commission was told. “Coram Children’s Legal Centre and Let Us Learn referred to longstanding and historic distrust of the Home Office amongst their client group,” the report says. Young and vulnerable asylum seekers and migrants expressed “anxiety at the decision-making process and the perception that the Home Office tries to refuse applications rather than looking to allow them.

“They referred to the high success rate in tribunal appeals. Similarly, the Joint Council for the Welfare of Immigrants expressed distrust of the culture within the Home Office, and the pressure under which caseworkers operate, saying that ‘caseworkers have very little training, are often very short term, and are under clear pressure, even if denied by ministers, to refuse applications’.”

The Law Commssion’s report is not itself a model of brevity: it runs to 220 pages.