LONDON, Aug 9 (Reuters) - British authorities arrested

almost one in five people they checked in a week-long crackdown

on migrants working illegally as delivery riders last month, the

government's interior ministry said on Saturday.

Immigration enforcement officers stopped and questioned

1,780 individuals between July 20 and 27 and 280 people were

arrested, the interior ministry said, adding asylum support was

being reviewed for 53 of those detained.

The operation was part of a push by the government to tackle

illegal migration which also includes new legal requirements for

companies to verify workers' immigration status.

Prime Minister Keir Starmer is facing pressure to show

voters he can counter illegal immigration with support rising

for Brexit campaigner Nigel Farage's Reform UK party.

"This government is making sure rules are respected and

enforced," border security minister Angela Eagle said.

As well as the arrests, civil penalty notices were issued to

51 businesses, including car washes and restaurants, which could

face fines for employing illegal workers, the ministry said.

Police seized 71 vehicles, including 58 e-bikes, and

confiscated 8,000 pounds ($10,751.20) in cash and 460,000 pounds

worth of illicit cigarettes.

The interior ministry said immigration enforcement teams

would receive a 5 million-pound funding boost for the work

tackling illegal working.

Last month, the government struck a new deal with food

delivery firms, including Deliveroo ( DROOF ), Uber Eats

and Just Eat, to share information aimed at preventing

illegal working.

In the 12 months to July, Britain returned 35,052 people

with no right to remain, up 13% on the previous 12 months.

France this week agreed to accept some undocumented migrants

who arrive in Britain by small boats with Britain accepting from

France an equal number of legitimate asylum seekers with family

ties in the country.

($1 = 0.7441 pounds)