Delivery company UK Mail has been accused of “ripping off” workers and using “inhuman” practices after it charged a courier nearly £800 when he was unable to work as a result of a car accident while on duty.

The £250m business, which delivers for retailers including Tesco, Homebase and O2, billed 47-year old Emil Ibrahimov £216 on the days he could not work after a car drove into him while he was carrying parcels from the rear of his van in east London.

In pain and with his leg swollen, he was taken to hospital by ambulance and told by doctors to rest and move only on crutches. But after he told his managers he could not work, UK Mail charged him, claiming it had to recoup the cost of finding a replacement courier.

Ibrahimov said he lost about £1,800 from taking seven days sick in the past 12 months when lost earnings and charges are added together. He has now quit.

Ibrahimov spoke out to the Guardian to highlight a practice that is understood to apply across UK Mail’s network of about 1,800 self-employed couriers. UK Mail made a profit of £16m profit last year when it was bought out by the Deutsche Post DHL Group.

The system of charges is written into the contracts of couriers who are paid per delivery. UK Mail also charged Ibrahimov when a doctor signed him off work for two weeks with acute back pain and sciatica caused by carrying heavy parcels. He went back to work after two days to avoid losses.

“I took my sick note in and they said it doesn’t matter because I am self-employed,” he said. “They did this to me and they will do it to someone else tomorrow and it is not right.”

The charges emerged amid growing concern at the treatment of self-employed couriers who supply the booming online shopping trade. The Guardian this month revealed DPD charges drivers £150 a day if they cannot find a replacement to cover their round and Royal Mail’s ParcelForce charges self-employed couriers up to £250 a day if they cannot find cover. On Wednesday, couriers at DPD’s Edinburgh depot staged a walkout after they were told they needed to work six days a week and in protest against charges.

Such charges are to be scrutinised by the Downing Street-commissioned review into modern employment practices led by Matthew Taylor.

Frank Field, the chair of the Commons work and pensions select committee, said he would press Taylor “to look closely at this rip-off practice which again shows how the odds are stacked against the low paid in Britain’s gig economy”.

Taylor said: “It is important that controversial practices in the modern labour market are made visible so that we can understand key challenges we need to address in our review.”

Frances O’Grady, general secretary of the Trades Union Congress, said UK Mail’s “punitive fines” were “a stark example of an employer reaping all the benefits of the gig economy, while the worker bears all the risk”.

She added: “Those in low-paid ‘self-employment’ pay a heavy price for falling sick. We need to crack down on bosses who do this.”

When a courier is sick, UK Mail pays them the amount earned by the replacement courier – in Ibrahimov’s case between £24 and £99 a day. But it also charges them whatever it costs to hire a replacement, which it said was £216 a day. For Ibrahimov it meant a net loss of £789 while he recovered from his work injury.

UK Mail denied it was ripping off workers. A spokesman said: “Subcontractors are made aware of the commercial nature of the agreement from the outset.

“UK Mail hasn’t profited out of this. They are simply covering the cost they have incurred finding cover for rounds.”

Tesco said it was “disappointed to hear of the treatment of this individual”, and O2 said it would “speak to UK Mail to understand more about their business operations for their self-employed drivers”. Homebase declined to comment.

Ibrahimov came to the UK from Azerbaijan six years ago and worked for UK Mail for two years, being paid per delivery stop. He said he typically worked five 12-hour days each week which, after expenses, saw him earn the equivalent under £7 an hour. The national minimum wage for over-24s is £7.20 but it does not apply to self-employed workers.

“Every day they were calling saying come to work,” Ibrahimov said of the aftermath of his car accident. “I would say I couldn’t and they would say I was going to be charged. So after a few days I had to go back. It was very painful but I had to go. It is inhuman because this happened while I was doing their job. The car accident didn’t stress me out as much as what UK Mail did afterwards.”

UK Mail declined to comment on Ibrahimov’s case but said: “UK Mail only ever passes on the actual costs incurred, which is in line with the contract with the driver and with company policy.

“On the rare occasions where a subcontractor fails to provide the agreed service by not making sure adequate cover is in place, UK Mail may be forced to make alternative arrangements … which are sometimes more expensive because of the short notice given. … UK Mail considers any such event individually.”