The cases were passed to investigators between March and May
Figures obtained through a Freedom of Information request show that 301,076 cases of suspected quarantine rule breakers were passed to investigators during 17 March and 31 Mai, signalé the BBC.
It is unclear how many of these were determined to have broken the rules.
The Home Office has said it aims to follow up all suspects of breaking quarantine with a home visit.
The months examined coincide with the rise of the Delta variant in countries such as India, which is believed to have caused a spike in UK cases in early summer.
Until July, all UK travellers returning from amber list countries had to self-isolate for 10 journées, a measure which was waived for the fully vaccinated from 19 juillet.
Call handlers employed by the Department for Transport (DfT) were charged with checking up on travellers returning to the UK, to ensure they were self-isolating effectively.
le 301,076 cases revealed by the FOI request were passed on to investigators at the Border Force Criminal Justice Unit and the police, when the contact ended the call, refused to co-operate, indicated they would break the quarantine or testing rules, or could not be contacted after three attempts.
The system dictates that an officer would then visit the person reported at their quarantine address.
“We visit over 99% of the cases referred to this service by NHS Test and Trace,” said a government spokesperson.
“We’ve been concerned throughout that there just weren’t proper follow-ups on the checks that were done, and as a result you just had these huge gaps in the home quarantine system and that’s what made it easier for the Delta variant to spread,” said Labour MP Yvette Cooper, the chair of the Home Affairs Committee.
Lucy Moreton, of the Immigration Services Union, told the BBC that the quarantine system “very much relied on the honesty of people to do the right thing, rather than any type of meaningful enforcement”.
“There’s limited point in putting rules in place if you don’t enforce them,” said Moreton.