Xanthe Couture, a Canadian living in the UK with her British husband, applied in March for indefinite leave to remain. The Home Office website said she would have to wait six months for a decision, but that if she paid an £800 super-priority premium on top of its £2,389 fee, she would hear back within one working day of submitting her biometric details.

Couture needed her residency permit swiftly to travel abroad for work, so she paid up. Five months passed before she heard her application had been successful. “The delay has meant I missed a summit I was a lead in organising and another important overseas meeting,” she says. “The uncertainty, the high costs and the lack of information from the Home Office have affected my mental health and my ability to do my job.”

Couture is one of a dozen readers who contacted the Observer after being left in limbo by Home Office delays, despite paying a small fortune for the heavily promoted super-priority service. The government outsourced its visa processing service to a French firm, Sopra Steria, last year and critics have accused the new system of letting down migrants with substandard service, despite fee increases introduced by the Home Office. Another company, VFS Global, was contracted to handle visa applications abroad and has also been criticised for alleged service failures.

Until last year, applicants in the UK could submit their ID and biometric data via their local post office, while those abroad could apply through a British embassy or consulate. Now overseas applicants are directed to hubs operated by Dubai-based VFS and those in the UK have to travel to one of six core centres, which offer a free service, or pay a minimum fee of £60 for an appointment at 51 others.

A shortage of free appointments has meant some have had to travel long distances or pay three-figure sums to complete their applications on time. Those without internet access are forced to book an appointment on a premium-rate phone line that costs £2.50 a minute, while an emailed query is charged at £5.48. Strict deadlines for submitting documents and data mean visa requests risk being rejected before applicants can secure an appointment, leaving them at risk of deportation unless they shell out for the premium service.

In June, Pakistani refugee Abdul Farooq was forced to beg contributions from friends to apply for the right to remain because there were no free appointments available within the six-week deadline. The only option was 200 miles away from his Manchester home and cost £780.

Those who pay the price for the fast-track option may be wasting their money. The Home Office says the 24-hour turnaround can’t be guaranteed if extra checks are required, but applicants have no way of predicting if those will be needed and report being left in the dark about their nature.

Only after querying the delay in a subject access request was Couture informed, two months later, that additional unspecified information was being sought. She says the requirements are so opaque that applicants have to employ a legal adviser if they want to be certain their application is comprehensive. “I have applied for several visas since 2011 and the situation is now really at breaking point, getting ever more expensive, unclear and essentially impossible,” she says. “The system seems to have been developed by people who don’t ever have to use government services for very serious life events that can alter the course of their lives.”

In 2014 the government announced plans to make the immigration system self-funding by 2020 through increased visa fees and a range of optional premium services. Since then the basic cost of applying for a settlement visa has increased 72% to £1,523. Now 6% of applicants pay up to £800 on top of that to avoid a six-month wait. Meanwhile, 21% of applicants from outside the UK paid the extra for premium services in 2017-18, according to Home Office figures, increasing the surplus from visa applications ninefold since the system was outsourced in 2014.

The government’s chief inspector of borders, David Bolt, accused it of devolving immigration services “on the cheap” without adequate oversight, while legal groups claim service levels have deteriorated as costs have increased. “We are concerned that these services may exploit vulnerable and less well-informed migrants, who may feel pressured to purchase an expensive service which will not provide them with any benefit, and we have been concerned about the poor level of service being provided by UK Visa and Immigration [UKVI] subcontractors for some time,” says Nicole Francis, chief executive of the Immigration Law Practitioners’ Association.

“The lack of transparency in the contractual arrangements between UKVI and the subcontractors were of particular concern. We have been worried the contract between UKVI and the subcontractors may have resulted in UKVI benefiting financially from the subcontractors selling additional services to customers.”

Applicants who felt pressured to pay the priority fee reported lost work, missed holidays and escalating costs as they awaited the decision on their status. Xiaoting Hou paid £3,208 for her visa application, including the £800 super-priority fee. “My job requires me to do a lot of international travel so I needed it quickly,” says the Chinese national who has lived in the UK for five years with her British husband. “The Home Office website states that I would be informed of any delays within a working day. In reality when you query progress with their contact centre, they require five working days to respond. After five working days, they simply say they can’t process the application on priority service standards, nor can they let you know which stage your application is at.”

It took three weeks for Hou to be informed that her application was successful. “It caused us a lot of sleepless nights,” she says. “My case should have been straightforward so I can only assume that the delay was because case workers are overworked and did not have capacity to carry out the super-priority service, although they won’t admit that.”

Taylor Maloney, a US national married to a Briton, was unable to take up a job offer because of months-long delays to her visa application, despite paying the £800 for a next-day decision. It eventually arrived 103 days later after the Observer took up her case. The Home Office blamed an “administrative error”.

Shailja Anand*, an Indian national with a British husband, waited six months for her spouse visa to be extended, despite paying for the priority service plus an extra £100 for an appointment at a processing centre in Croydon to avoid a two-week wait for a free one. “I needed my visa as quickly as possible for work and to sponsor my family who were coming over,” she says. “I received the decision granting me further leave to remain within 24 hours by email and was told my biometric residency permit should reach me within 10 working days.” The permit didn’t arrive and Anand eventually discovered her biometrics had not been processed correctly. She was told to make the long journey back to Croydon for another appointment and received her visa too late for her family’s visit.

MPs have called for an independent review into the privatised visa system. The Home Office denies that there is a problem and says it regularly reviews the availability of free appointments for applicants. “We are committed to providing a world-class service to people using our visa systems,” it says. “Our [web] page makes clear that the super-priority service can take longer if we require additional information. We work closely with our partners to provide excellent customer service and the vast majority of applications are processed in line with service standards.” Hou, Anand and Maloney have since received refunds of their super-premium fee.

Sopra Steria did not respond to specific questions about lack of free appointments and the promotion of add-on services. “Applicants can select a free or paid appointment to submit their biometric data, depending on availability. A paid appointment can cost anywhere from £65 at a core or enhanced service point, to a maximum of £260 for an appointment at a premium lounge,” it said. “The super-priority service offers a decision within one working day of an applicant submitting their biometric data via an appointment at a centre.” VFS Global also omitted to respond to specific questions about its charges, profits and performance. It said: “The super-priority visa and priority visa services are optional services offered by UK Visas and Immigration.”

* This name has been changed