The home office said that their document are checked, the demeanour and physical appearance by 2 yes 2 social workers who then had to sign off on them being under 18
I can't comment on the documents thing, but if social workers are unable to see that some of these "children" are clearly well into adulthood, I'd suggest that either questions need to be asked about their competence - or maybe even about who's pressuring them to make such decisions? 
Medical and dental checks were not carried out as they are too intrusive, according to the home office
And if this is true, the Home Office need their arses kicking. I appreciate dental checks aren't exact (though it's pretty close according to gov.uk, which says: The margin of error ... is approximately plus or minus 2 years or less, for 95% of the population) but given what's at stake, anyone who describes having teeth looked at or wrists x-rayed as "intrusive" needs a reality check IMHO